Prepare for other years

2020/src/main/kotlin/Day01.kt

@@ -0,0 +1,32 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+
+@Day(1)
+class Day01(@Lines input: Input<IntArray>) {
+    private val items = input.value
+
+    fun part1(): Int? {
+        items.forEach { a ->
+            items.forEach { b ->
+                if (a + b == 2020) return a * b
+            }
+        }
+        return null
+    }
+
+    fun part2(): Int? {
+        items.forEach { a ->
+            items.forEach { b ->
+                items.forEach { c ->
+                    if (a + b + c == 2020) return a * b * c
+                }
+            }
+        }
+        return null
+    }
+
+}
+

2020/src/main/kotlin/Day02.kt

@@ -0,0 +1,23 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+
+@Day(2)
+class Day02(@Lines input: Input<List<String>>) {
+    private data class PasswordEntry(val range: IntRange, val letter: Char, val password: String)
+
+    private val regex = "^(\\d+)-(\\d+) ([a-z]): (.*)$".toRegex()
+
+    private val passwords = input.value.map {
+        val (_, min, max, letter, password) = regex.find(it)!!.groupValues
+        PasswordEntry(min.toInt()..max.toInt(), letter[0], password)
+    }
+
+    fun part1() = passwords.count { it.password.count { char -> char == it.letter } in it.range }
+
+    fun part2() = passwords.count { (range, letter, pwd) ->
+        (pwd[range.first - 1] == letter) xor (pwd[range.last - 1] == letter)
+    }
+}

2020/src/main/kotlin/Day03.kt

@@ -0,0 +1,40 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+
+@Day(3)
+class Day03(@Lines val input: Input<List<String>>) {
+    private data class Slope(val x: Int, val y: Int)
+
+    private fun findSlope(slope: Slope): Int {
+        val grid = input.value
+        var trees = 0
+        var x = 0
+        var y = 0
+
+        val width = grid.first().length
+
+        while (y < grid.size - 1) {
+            x += slope.x
+            y += slope.y
+
+            if (grid[y][x % width] == '#') trees++
+        }
+
+        return trees
+    }
+
+    fun part1() = findSlope(Slope(x = 3, y = 1))
+
+    fun part2(): Long = listOf(
+        Slope(x = 1, y = 1),
+        Slope(x = 3, y = 1),
+        Slope(x = 5, y = 1),
+        Slope(x = 7, y = 1),
+        Slope(x = 1, y = 2),
+    )
+        .map { findSlope(it).toLong() }
+        .reduce { acc, trees -> acc * trees }
+}

2020/src/main/kotlin/Day04.kt

@@ -0,0 +1,43 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Text
+
+private typealias Entry = Pair<String, String>
+private typealias Entries = List<Entry>
+
+@Day(4)
+class Day04(@Text val input: Input<String>) {
+
+    val entries = input.value.split("\n\n").map {
+        it.split(" ", "\n").map { it.split(":").let { (k, v) -> k to v } }
+    }
+
+    private fun Entries.hasRequiredKeys() = map { it.first }
+        .containsAll(listOf("byr", "iyr", "eyr", "hgt", "hcl", "ecl", "pid"))
+
+    fun part1() = entries.count { it.hasRequiredKeys() }
+
+    private val hclRegex = Regex("#[0-9a-f]{6}")
+    private val pidRegex = Regex("[0-9]{9}")
+
+    private fun Entry.isValid() = let { (k, v) ->
+        when (k) {
+            "byr" -> v.toInt() in 1920..2002
+            "iyr" -> v.toInt() in 2010..2020
+            "eyr" -> v.toInt() in 2020..2030
+            "hgt" -> when {
+                v.endsWith("cm") -> v.removeSuffix("cm").toInt() in 150..193
+                v.endsWith("in") -> v.removeSuffix("in").toInt() in 59..76
+                else -> false
+            }
+            "hcl" -> v.matches(hclRegex)
+            "ecl" -> v in arrayOf("amb", "blu", "brn", "gry", "grn", "hzl", "oth")
+            "pid" -> v.matches(pidRegex)
+            else -> true
+        }
+    }
+
+    fun part2() = entries.count { it.hasRequiredKeys() && it.all { it.isValid() } }
+}

2020/src/main/kotlin/Day05.kt

@@ -0,0 +1,23 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+
+@Day(5)
+class Day05(@Lines val input: Input<List<String>>) {
+
+    private val ids = input.value.map {
+        it.replace("F", "0")
+            .replace("B", "1")
+            .replace("L", "0")
+            .replace("R", "1")
+            .toInt(2)
+    }.sorted()
+
+    fun part1() = ids.last()
+
+    fun part2() = ids.windowed(size = 2, step = 1)
+        .find { (a, b) -> b - a > 1 }!!
+        .first() + 1
+}

2020/src/main/kotlin/Day06.kt

@@ -0,0 +1,24 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Text
+import org.eclipse.collections.impl.factory.primitive.CharBags
+
+@Day(6)
+class Day06(@Text val input: Input<String>) {
+
+    private val groups = input.value.split("\n\n")
+
+    fun part1() = groups.sumBy { it.replace("\n", "").toCharArray().toSet().size }
+
+    fun part2() = groups.sumBy {
+        val group = it.split("\n")
+        val bag = CharBags.mutable.empty()
+
+        group.forEach { chars: String -> chars.forEach { bag.add(it) } }
+
+        bag.selectByOccurrences { group.size == it }.toSet().size()
+    }
+
+}

2020/src/main/kotlin/Day07.kt

@@ -0,0 +1,51 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+import org.eclipse.collections.api.factory.Stacks
+import org.eclipse.collections.api.multimap.list.ImmutableListMultimap
+import org.eclipse.collections.api.stack.MutableStack
+import org.eclipse.collections.impl.factory.Multimaps
+
+@Day(7)
+class Day07(@Lines val input: Input<List<String>>) {
+
+    private data class Bag(val count: Int, val color: String)
+
+    private val map: ImmutableListMultimap<String, Bag>
+
+    init {
+        val mutableMap = Multimaps.mutable.list.empty<String, Bag>()
+
+        val colorRegex = "^(\\w+ \\w+)".toRegex()
+        val requirementRegex = "(\\d+) (\\w+ \\w+) bag".toRegex()
+
+        for (line in input.value) {
+            val outerColor = colorRegex.find(line)!!.groupValues[1]
+            for (match in requirementRegex.findAll(line)) {
+                val (_, count, color) = match.groupValues
+                mutableMap.put(outerColor, Bag(count.toInt(), color))
+            }
+        }
+
+        map = mutableMap.toImmutable()
+    }
+
+    private fun bagSequence(rootColor: String): Sequence<Bag> = sequence {
+        val stack: MutableStack<Bag> = Stacks.mutable.ofAll(map.get(rootColor))
+        while (stack.notEmpty()) {
+            val current = stack.pop().also { yield(it) }
+            map[current.color]?.let {
+                it.forEach { (count, color) ->
+                    stack.push(Bag(current.count * count, color))
+                }
+            }
+        }
+    }
+
+    fun part1() = map.keySet().count { bagSequence(it).any { it.color == "shiny gold" } }
+
+    fun part2() = bagSequence("shiny gold").sumBy { it.count }
+
+}

2020/src/main/kotlin/Day08.kt

@@ -0,0 +1,76 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+import org.eclipse.collections.impl.factory.primitive.IntLists
+import org.eclipse.collections.impl.factory.primitive.IntSets
+
+@Day(8)
+class Day08(@Lines val input: Input<List<String>>) {
+
+    private val instructions = input.value.map {
+        val words = it.split(" ")
+        Instruction(Operation.valueOf(words[0].capitalize()), words[1].toInt())
+    }.toTypedArray()
+
+    fun part1() = run(instructions).let {
+        when (it) {
+            is VmResult.Looped -> it.acc
+            is VmResult.Terminated -> it.acc
+        }
+    }
+
+    private fun run(instructions: Array<Instruction>): VmResult {
+        var acc = 0
+        var ptr = 0
+
+        val visited = IntSets.mutable.empty()
+
+        while (visited.add(ptr)) {
+            val instruction = instructions[ptr]
+            when (instruction.operation) {
+                Operation.Acc -> {
+                    acc += instruction.argument
+                    ptr++
+                }
+                Operation.Jmp -> ptr += instruction.argument
+                Operation.Nop -> ptr++
+            }
+            if (ptr !in instructions.indices) {
+                return VmResult.Terminated(acc)
+            }
+        }
+
+        return VmResult.Looped(acc)
+    }
+
+    fun part2(): Int {
+        val possibleMutations = IntLists.mutable.empty()
+        instructions.forEachIndexed { i, e ->
+            if (e.operation == Operation.Jmp || e.operation == Operation.Nop) possibleMutations.add(i)
+        }
+
+        for (index in possibleMutations.toArray()) {
+            val copy = instructions.copyOf().also {
+                val modifiedOperation = if (it[index].operation == Operation.Nop) Operation.Jmp else Operation.Nop
+                it[index] = it[index].copy(operation = modifiedOperation)
+            }
+
+            val res = run(copy)
+            if (res is VmResult.Terminated) return res.acc
+        }
+
+        error("No result found")
+    }
+
+}
+
+private enum class Operation { Acc, Jmp, Nop }
+
+private data class Instruction(val operation: Operation, val argument: Int)
+
+private sealed class VmResult {
+    data class Looped(val acc: Int) : VmResult()
+    data class Terminated(val acc: Int) : VmResult()
+}

2020/src/main/kotlin/Day09.kt

@@ -0,0 +1,50 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+
+@Day(9)
+class Day09(@Lines val input: Input<LongArray>) {
+
+    private var part1Result = 0L
+
+    fun part1(): Long? {
+        val longs = input.value
+
+        for (windowStart in 0 until longs.size - 26) {
+            val last = longs[windowStart + 25]
+            if (!isValid(windowStart, last)) {
+                part1Result = last
+                return last
+            }
+        }
+
+        return null
+    }
+
+    private fun isValid(windowStart: Int, last: Long): Boolean {
+        for (i in windowStart until windowStart + 25) {
+            for (j in windowStart + 1 until windowStart + 25) {
+                val f = input.value[i]
+                val s = input.value[j]
+                if (f + s == last && f != s) return true
+            }
+        }
+        return false
+    }
+
+    fun part2(): Long {
+        var size = 2
+        while (true) {
+            for (startIndex in input.value.indices) {
+                val lastIndex = input.value.size - 1 - size
+                if (startIndex + size > lastIndex) break
+                val slice = input.value.sliceArray(startIndex..startIndex + size)
+                if (slice.sum() == part1Result) return slice.minOrNull()!! + slice.maxOrNull()!!
+            }
+            size++
+        }
+    }
+
+}

2020/src/main/kotlin/Day10.kt

@@ -0,0 +1,44 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+import org.eclipse.collections.api.list.primitive.MutableIntList
+import org.eclipse.collections.impl.factory.primitive.IntLists
+import org.eclipse.collections.impl.factory.primitive.IntLongMaps
+
+@Day(10)
+class Day10(@Lines val input: Input<IntArray>) {
+
+    fun part1(): Int {
+        val sorted = IntLists.mutable.of(0, *input.value).apply {
+            sortThis()
+            add(last + 3)
+        }.toArray().toList()
+
+        var ones = 0
+        var threes = 0
+
+        sorted.zipWithNext().forEach { (a, b) ->
+            if (a + 1 == b) ones++
+            else if (a + 3 == b) threes++
+        }
+
+        return ones * threes
+    }
+
+    fun part2(): Long {
+        val sorted: MutableIntList = IntLists.mutable.of(*input.value).apply { sortThis() }
+
+        val map = IntLongMaps.mutable.empty().apply {
+            put(0, 1L)
+        }
+
+        sorted.forEach { i ->
+            map.put(i, map.get(i - 1) + map.get(i - 2) + map.get(i - 3))
+        }
+
+        return map.get(sorted.last)
+    }
+
+}

2020/src/main/kotlin/Day11.kt

@@ -0,0 +1,117 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+
+private typealias Seats = Array<CharArray>
+
+private fun Seats.deepClone(): Seats = map { it.clone() }.toTypedArray()
+
+private operator fun Seats.get(x: Int, y: Int): Char = this[y][x]
+private operator fun Seats.set(x: Int, y: Int, value: Char) {
+    this[y][x] = value
+}
+
+private operator fun Seats.contains(xy: Pair<Int, Int>): Boolean {
+    val (x, y) = xy
+    return x in 0 until width && y in 0 until height
+}
+
+private val Seats.width get() = first().size
+private val Seats.height get() = size
+
+private fun Seats.asGridString() = joinToString("\n") { it.joinToString("") }
+private fun Seats.countOccupied() = sumBy { it.count { it == '#' } }
+
+@Day(11)
+class Day11(@Lines val input: Input<List<String>>) {
+
+    private val seats: Seats = input.value.map { it.toCharArray() }.toTypedArray()
+
+    private val directions = listOf(
+        -1 to -1,
+        +0 to -1,
+        +1 to -1,
+        +1 to +0,
+        +1 to +1,
+        +0 to +1,
+        -1 to +1,
+        -1 to +0,
+    )
+
+    private fun countAdjacentOccupiedSeats(x: Int, y: Int, seats: Array<CharArray>): Int =
+        directions.mapNotNull { (dx, dy) ->
+            val xx = x + dx
+            val yy = y + dy
+
+            if (xx to yy in seats) seats[xx, yy]
+            else null
+        }.count { it == '#' }
+
+    private fun countVisibleOccupiedSeats(x: Int, y: Int, seats: Seats): Int {
+        var occupied = 0
+
+        for ((dx, dy) in directions) {
+            var xx = x
+            var yy = y
+            while (true) {
+                xx += dx
+                yy += dy
+                if (xx to yy !in seats) break
+                if (seats[xx, yy] == 'L') break
+                if (seats[xx, yy] == '#') {
+                    occupied++
+                    break
+                }
+            }
+        }
+
+        return occupied
+    }
+
+    private fun findLastRepeating(seats: Seats, next: (Seats) -> Seats): Seats {
+        var previous = seats
+        val set = HashSet<String>() // use strings because Arrays don't implement equals ??
+
+        while (true) {
+            val res = next(previous)
+            if (!set.add(res.asGridString())) return res
+            previous = res
+        }
+    }
+
+    private fun progress1(previous: Array<CharArray>): Array<CharArray> {
+        val next = previous.deepClone()
+
+        for (x in 0 until seats.width) {
+            for (y in 0 until seats.height) {
+                when (previous[x, y]) {
+                    'L' -> if (countAdjacentOccupiedSeats(x, y, previous) == 0) next[x, y] = '#'
+                    '#' -> if (countAdjacentOccupiedSeats(x, y, previous) >= 4) next[x, y] = 'L'
+                }
+            }
+        }
+
+        return next
+    }
+
+    fun part1() = findLastRepeating(seats, ::progress1).countOccupied()
+
+    private fun progress2(previous: Seats): Array<CharArray> {
+        val next = previous.deepClone()
+
+        for (x in 0 until previous.width) {
+            for (y in 0 until previous.height) {
+                when (previous[x, y]) {
+                    'L' -> if (countVisibleOccupiedSeats(x, y, previous) == 0) next[x, y] = '#'
+                    '#' -> if (countVisibleOccupiedSeats(x, y, previous) >= 5) next[x, y] = 'L'
+                }
+            }
+        }
+        return next
+    }
+
+    fun part2() = findLastRepeating(seats, ::progress2).countOccupied()
+
+}

2020/src/main/kotlin/Day12.kt

@@ -0,0 +1,80 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+import kotlin.math.abs
+
+@Day(12)
+class Day12(@Lines val input: Input<List<String>>) {
+
+    fun part1(): Int {
+        var x = 0
+        var y = 0
+        var facing = "E"
+
+        val dirs = listOf("N", "E", "S", "W")
+
+        input.value.forEach {
+            val dir = it.take(1)
+            val steps = it.drop(1).toInt()
+
+            when (dir) {
+                "L" -> repeat(steps / 90) {
+                    val i = (dirs.indexOf(facing) + 4 - 1) % 4
+                    facing = dirs[i]
+                }
+                "R" -> repeat(steps / 90) {
+                    val i = (dirs.indexOf(facing) + 1) % 4
+                    facing = dirs[i]
+                }
+            }
+
+            when (if (dir == "F") facing else dir) {
+                "N" -> y -= steps
+                "S" -> y += steps
+                "W" -> x -= steps
+                "E" -> x += steps
+            }
+
+        }
+
+        return abs(x) + abs(y)
+    }
+
+    fun part2(): Int {
+        var x = 0
+        var y = 0
+
+        var waypointX = 10
+        var waypointY = -1
+
+        input.value.forEach {
+            val dir = it.take(1)
+            val steps = it.drop(1).toInt()
+
+            when (dir) {
+                "L" -> repeat(steps / 90) {
+                    val oldY = waypointY
+                    waypointY = -waypointX
+                    waypointX = oldY
+                }
+                "R" -> repeat(steps / 90) {
+                    val oldY = waypointY
+                    waypointY = waypointX
+                    waypointX = -oldY
+                }
+                "F" -> {
+                    x += waypointX * steps
+                    y += waypointY * steps
+                }
+                "N" -> waypointY -= steps
+                "S" -> waypointY += steps
+                "W" -> waypointX -= steps
+                "E" -> waypointX += steps
+            }
+        }
+
+        return abs(x) + abs(y)
+    }
+}

2020/src/main/kotlin/Day13.kt

@@ -0,0 +1,49 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+import kotlin.math.abs
+
+private data class Bus(val index: Int, val id: Long)
+
+@Day(13)
+class Day13(@Lines val input: Input<List<String>>) {
+
+    fun part1(): Int {
+        val id = input.value[0].toInt()
+
+        val (busId, min) = input.value[1]
+            .splitToSequence(",")
+            .filterNot { it == "x" }
+            .map { it.toInt() }
+            .map { bus -> bus to id / bus }
+            .map { (bus, div) -> bus to bus * (div + 1) }
+            .minByOrNull { it.second }!!
+
+        return busId * abs(min - id)
+    }
+
+    private tailrec fun gcd(a: Long, b: Long): Long = if (b == 0L) a else gcd(b, a % b)
+    private fun lcm(a: Long, b: Long): Long = a / gcd(a, b) * b
+
+    fun part2(): Long {
+        val buses = input.value[1]
+            .splitToSequence(",")
+            .mapIndexedNotNull { index, bus ->
+                if (bus == "x") null
+                else Bus(index, bus.toLong())
+            }
+            .toList()
+
+        var step = 1L
+        var t = 0L
+
+        for ((i, id) in buses) {
+            while ((t + i) % id != 0L) t += step
+            step = lcm(step, id)
+        }
+
+        return t
+    }
+}

2020/src/main/kotlin/Day14.kt

@@ -0,0 +1,94 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+import kotlin.math.pow
+import org.eclipse.collections.impl.factory.primitive.IntObjectMaps
+import org.eclipse.collections.impl.factory.primitive.LongIntMaps
+
+@Day(14)
+class Day14(@Lines val input: Input<List<String>>) {
+
+    private val memRe = "mem\\[(\\d+)] = (.*)$".toRegex()
+
+    private fun Long.toBin36() = toString(2).padStart(length = 36, padChar = '0')
+
+    fun part1(): Long {
+        val mem = IntObjectMaps.mutable.empty<String>()
+
+        var currentMask: String = ""
+
+        for (line in input.value) {
+            if (line.startsWith("mask")) {
+                currentMask = line.removePrefix("mask = ")
+            } else {
+                val (address, value) = memRe.find(line)!!.destructured
+                val bin = value.toLong().toBin36()
+
+                val result = bin.zip(currentMask)
+                    .map { (bin, mask) -> if (mask != 'X') mask else bin }
+                    .joinToString("")
+
+                mem.put(address.toInt(), result)
+            }
+        }
+
+        return mem.values()
+            .map { it.dropWhile { it == '0' } }
+            .map { it.toLong(2) }
+            .sum()
+    }
+
+    fun part2(): Long {
+        val mem = LongIntMaps.mutable.empty()
+
+        var currentMask = ""
+
+        for (line in input.value) {
+            if (line[1] == 'a') {
+                currentMask = line.substring(7)
+            } else {
+
+                val (address, value) = memRe.find(line)!!.destructured.let { (add, value) ->
+                    add.toLong().toBin36() to value.toInt()
+                }
+
+                val mutations = generateMutations(currentMask, address)
+
+                for (mutation in mutations) {
+                    mem.put(String(mutation).toLong(2), value)
+                }
+            }
+        }
+
+        return mem.values().sum()
+    }
+
+    private fun generateMutations(mask: String, address: String): Array<CharArray> {
+        val mutationCount = mask.count { it == 'X' }.let { 2.0.pow(it.toDouble()).toInt() }
+        val mutations = Array(mutationCount) { CharArray(36) }
+
+        var groups = 1
+
+        for (i in mask.indices) {
+            when (mask[i]) {
+                'X' -> {
+                    groups *= 2
+                    val groupSize = mutationCount / groups
+                    var currentChar = '1'
+                    for (b in mutations.indices) {
+                        val builder = mutations[b]
+                        val flip = b % groupSize == 0
+                        if (flip) currentChar = if (currentChar == '0') '1' else '0'
+                        builder[i] = currentChar
+                    }
+                }
+                '1' -> mutations.forEach { it[i] = '1' }
+                else -> mutations.forEach { it[i] = address[i] }
+            }
+        }
+        return mutations
+    }
+
+}

2020/src/main/kotlin/Day15.kt

@@ -0,0 +1,44 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Csv
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import kotlin.math.abs
+import org.eclipse.collections.impl.factory.primitive.IntObjectMaps
+
+@Day(15)
+class Day15(@Csv val input: Input<IntArray>) {
+
+    private fun run(until: Int): Int {
+        val start = input.value
+
+        val map = IntObjectMaps.mutable.empty<IntArray>()
+
+        var last = -1
+
+        fun say(round: Int, number: Int) {
+            val lastValues = map.get(number)
+            val values = lastValues
+                ?.let { intArrayOf(round, it.maxOrNull()!!) }
+                ?: intArrayOf(round)
+
+            map.put(number, values)
+            last = number
+        }
+
+        for (i in 1..until) {
+            if (i <= start.size) {
+                say(i, start[i - 1])
+            } else {
+                val lastValues = map.get(last)
+                if (lastValues?.size ?: 0 < 2) say(i, 0)
+                else say(i, abs(lastValues[0] - lastValues[1]))
+            }
+        }
+        return last
+    }
+
+    fun part1() = run(until = 2020)
+
+    fun part2() = run(until = 30000000)
+}

2020/src/main/kotlin/Day16.kt

@@ -0,0 +1,149 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Groups
+import be.vandewalleh.aoc.utils.input.Input
+import org.eclipse.collections.api.multimap.list.ListMultimap
+import org.eclipse.collections.api.multimap.list.MutableListMultimap
+import org.eclipse.collections.api.multimap.set.MutableSetMultimap
+import org.eclipse.collections.impl.factory.Multimaps
+import org.eclipse.collections.impl.multimap.list.FastListMultimap
+
+@Day(16)
+class Day16(@Groups val input: Input<List<List<String>>>) {
+
+    private val rangesGroup = input.value[0]
+    private val myTicket = input.value[1][1]
+    private val nearbyTicketsGroup = input.value[2].drop(1)
+
+    private val rangeRe = "(\\d+)-(\\d+)".toRegex()
+
+    private fun extractRanges(line: String): Sequence<IntRange> = rangeRe.findAll(line)
+        .map {
+            val (min, max) = it.destructured
+            min.toInt()..max.toInt()
+        }
+
+    fun part1(): Int {
+        val minMax = mutableListOf<IntRange>()
+
+        for (line in rangesGroup) {
+            minMax.addAll(extractRanges(line))
+        }
+
+        val nearbyTickets = mutableListOf<Int>()
+        for (line in nearbyTicketsGroup) {
+            line.splitToSequence(",").forEach { nearbyTickets.add(it.toInt()) }
+        }
+
+        val invalid = mutableListOf<Int>()
+        nearbyTickets.forEach { number ->
+            if (minMax.none { number in it }) invalid.add(number)
+        }
+
+        return invalid.sum()
+    }
+
+    private fun isTicketValid(ticket: List<Int>, ranges: Iterable<IntRange>): Boolean {
+        for (number in ticket) {
+            if (!ranges.any { number in it }) return false
+        }
+        return true
+    }
+
+    private fun inRanges(value: Int, ranges: List<IntRange>) = ranges.any { value in it }
+
+    fun part2(): Long {
+        val rangesByName = namedRanges()
+        val validTickets = validTickets(rangesByName)
+        val indexesByCategory = indexesByCategory(rangesByName, validTickets)
+
+        removeDuplicates(indexesByCategory)
+
+        val myTicketValues = myTicket.split(",").map { it.toInt() }
+
+        var mult = 1L
+        indexesByCategory.forEachKeyValue { category, index ->
+            if (category.startsWith("departure")) {
+                mult *= myTicketValues[index]
+            }
+        }
+        return mult
+    }
+
+    private fun removeDuplicates(indexesByCategory: MutableSetMultimap<String, Int>) {
+        val toBeRemoved = HashSet<Int>()
+        val queue = ArrayDeque<Int>()
+
+        indexesByCategory.multiValuesView()
+            .toSortedListBy { it.size() }
+            .forEach { it.forEach { if (toBeRemoved.add(it)) queue.add(it) } }
+
+        queue.removeLast()
+
+        val categoriesToRemove = mutableListOf<String>()
+
+        while (queue.isNotEmpty()) {
+            val duplicate = queue.removeFirst()
+
+            categoriesToRemove.clear()
+
+            for (entry in indexesByCategory.keyMultiValuePairsView()) {
+                if (entry.two.size() < 2) continue
+                categoriesToRemove.add(entry.one)
+            }
+
+            for (category in categoriesToRemove) {
+                indexesByCategory.remove(category, duplicate)
+            }
+        }
+    }
+
+    private fun indexesByCategory(
+        rangesByName: ListMultimap<String, IntRange>,
+        validTickets: List<List<Int>>,
+    ): MutableSetMultimap<String, Int> {
+        val indexesByCategory = Multimaps.mutable.set.empty<String, Int>()
+
+        for (entry in rangesByName.keyMultiValuePairsView()) {
+            val category = entry.one
+            val ranges = entry.two.toList()
+
+            for (i in validTickets.first().indices) {
+                var allInRange = true
+                for(ticket in validTickets){
+                    val current = ticket[i]
+                    if(!inRanges(current, ranges)){
+                        allInRange = false
+                        break
+                    }
+                }
+                if (allInRange) indexesByCategory.put(category, i)
+            }
+        }
+        return indexesByCategory
+    }
+
+    private fun validTickets(rangesByName: MutableListMultimap<String, IntRange>): List<List<Int>> {
+        val validTickets = mutableListOf<List<Int>>()
+        val ranges = rangesByName.valuesView().toList()
+        for (line in nearbyTicketsGroup) {
+            val ticket = line.split(",").map { it.toInt() }
+            if (isTicketValid(ticket, ranges)) {
+                validTickets.add(ticket)
+            }
+        }
+        return validTickets
+    }
+
+    private fun namedRanges(): MutableListMultimap<String, IntRange> {
+        val rangesByName = FastListMultimap<String, IntRange>()
+        for (line in rangesGroup) {
+            val name = line.substringBefore(":")
+            extractRanges(line).forEach {
+                rangesByName.put(name, it)
+            }
+        }
+        return rangesByName
+    }
+}

2020/src/main/kotlin/Day17.kt

@@ -0,0 +1,88 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+
+private data class Point(val x: Int, val y: Int, val z: Int)
+private data class Point4(val x: Int, val y: Int, val z: Int, val blah: Int)
+
+private enum class State { Active, Inactive }
+
+@Day(17)
+class Day17(@Lines val input: Input<List<String>>) {
+
+    fun part1(): Int {
+        val grid = parseGrid { x, y -> Point(x, y, 0) }
+        repeat(6) { step(grid, ::neighbours3) }
+        return grid.values.count { it == State.Active }
+    }
+
+    fun part2(): Int {
+        val grid = parseGrid { x, y -> Point4(x, y, 0, 0) }
+        repeat(6) { step(grid, ::neighbours4) }
+        return grid.values.count { it == State.Active }
+    }
+
+    private fun <T> parseGrid(pointFactory: (x: Int, y: Int) -> T): MutableMap<T, State> {
+        val grid = mutableMapOf<T, State>()
+        input.value.forEachIndexed { index, row ->
+            row.forEachIndexed { col, char ->
+                val state = if (char == '#') State.Active else State.Inactive
+                grid[pointFactory(index, col)] = state
+            }
+        }
+        return grid
+    }
+
+    private fun <T> step(grid: MutableMap<T, State>, neighbours: (T) -> List<T>) {
+        val modifications = mutableMapOf<T, State>()
+        val pointsToConsider = grid.keys.flatMap { neighbours(it) }.toSet()
+        for (point in pointsToConsider) {
+            val neighbours = neighbours(point)
+            val activeNeighboursCount = neighbours.count { grid[it] ?: State.Inactive == State.Active }
+            val state = grid[point] ?: State.Inactive
+            if (state == State.Active && activeNeighboursCount !in 2..3) {
+                modifications[point] = State.Inactive
+            } else if (activeNeighboursCount == 3) {
+                modifications[point] = State.Active
+            }
+        }
+        for ((point, state) in modifications) {
+            grid[point] = state
+        }
+    }
+
+    private fun neighbours3(point: Point): List<Point> {
+        val points = mutableListOf<Point>()
+        for (x in point.x - 1..point.x + 1) {
+            for (y in point.y - 1..point.y + 1) {
+                for (z in point.z - 1..point.z + 1) {
+                    val generatedPoint = Point(x, y, z)
+                    if (generatedPoint != point)
+                        points.add(generatedPoint)
+                }
+            }
+        }
+        check(points.size == 26) { "Points size was ${points.size}" }
+        return points
+    }
+
+    private fun neighbours4(point: Point4): List<Point4> {
+        val points = mutableListOf<Point4>()
+        for (x in point.x - 1..point.x + 1) {
+            for (y in point.y - 1..point.y + 1) {
+                for (z in point.z - 1..point.z + 1) {
+                    for (blah in point.blah - 1..point.blah + 1) {
+                        val generatedPoint = Point4(x, y, z, blah)
+                        if (generatedPoint != point)
+                            points.add(generatedPoint)
+                    }
+                }
+            }
+        }
+        check(points.size == 80) { "Points size was ${points.size}" }
+        return points
+    }
+
+}

2020/src/main/kotlin/Day18.kt

@@ -0,0 +1,171 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+import java.util.*
+import org.slf4j.Logger
+import org.slf4j.LoggerFactory
+
+private enum class Operator { Add, Multiply }
+
+private operator fun Operator.invoke(a: Long, b: Long) = when (this) {
+    Operator.Add -> a + b
+    Operator.Multiply -> a * b
+}
+
+private inline fun Logger.debug(msg: () -> Any) {
+    if (isDebugEnabled) debug(msg().toString())
+}
+
+@Day(18)
+class Day18(@Lines val input: Input<List<String>>) {
+
+    private val logger = LoggerFactory.getLogger("Day18")
+    private val lines = input.value.map { it.replace(" ", "") }
+
+    private fun parseGroups(line: String): Map<Int, List<IntRange>> {
+        var depth = 0
+        val groups = mutableMapOf<Int, MutableList<IntRange>>()
+        val openingPars = Stack<Int>()
+
+        for ((index, char) in line.withIndex()) {
+            when (char) {
+                '(' -> {
+                    openingPars.push(index)
+                    depth++
+                }
+                ')' -> {
+                    depth--
+                    val group = groups.getOrPut(depth) { mutableListOf() }
+                    group.add(openingPars.pop()..index)
+                }
+            }
+        }
+
+        return groups.also { logger.debug { it } }
+    }
+
+    private fun solveGroup(group: String, precedence: Boolean) = solveGroup(parseGroup(group), precedence)
+
+    private fun solveGroup(group: Pair<LinkedList<Long>, LinkedList<Operator>>, precedence: Boolean): Long {
+        val (operands, operators) = group
+        logger.debug { operands }
+        logger.debug { operators }
+
+        if (!precedence) {
+            for (i in operators.indices) {
+                val a = operands[i]
+                val b = operands[i + 1]
+
+                val result = operators[i](a, b)
+
+                operands[i + 1] = result
+            }
+
+            return operands.peekLast()
+        } else {
+
+            var i = 0
+            while (operators.any { it == Operator.Add }) {
+
+                val operator = operators[i]
+
+                if (operator == Operator.Add) {
+                    val a = operands[i]
+                    val b = operands[i + 1]
+                    val res = operator(a, b)
+                    operands.removeAt(i)
+                    operands[i] = res
+                    operators.removeAt(i)
+                } else {
+                    i++
+                }
+            }
+
+            return operands.reduce { a, b -> Operator.Multiply(a, b) }
+        }
+    }
+
+    private fun parseGroup(group: String): Pair<LinkedList<Long>, LinkedList<Operator>> {
+        val operands = LinkedList<Long>()
+        val operators = LinkedList<Operator>()
+        val operand = StringBuilder()
+
+        for (char in group) {
+            if (char.isDigit()) {
+                operand.append(char)
+            } else {
+                val operator = when (char) {
+                    '+' -> Operator.Add
+                    '*' -> Operator.Multiply
+                    else -> error("Unknown operator $char")
+                }
+                operators.add(operator)
+                operands.add(operand.toString().toLong())
+                operand.clear()
+            }
+        }
+
+        operands.add(operand.toString().toLong())
+
+        return Pair(operands, operators)
+    }
+
+    private fun solveLine(line: String, precedence: Boolean = false): Long {
+        var l = line
+
+        while (true) {
+            val groups = parseGroups(l)
+            if (groups.isEmpty()) break
+
+            val highestDepth = groups.keys.maxOrNull()!!
+            val solvableRanges = groups[highestDepth]!!
+
+            val solved = ArrayDeque<Pair<IntRange, Long>>()
+
+            for (range in solvableRanges) {
+                val rangeWithoutPars = range.first + 1 until range.last
+                val answer = solveGroup(l.substring(rangeWithoutPars), precedence)
+                solved.addLast(range to answer)
+            }
+
+            var solution = solved.removeFirst()
+            var inside = false
+
+            val builder = StringBuilder()
+
+            for (i in l.indices) {
+                if (!inside && i in solution.first) {
+                    inside = true
+                    builder.append(solution.second)
+                } else if (inside && i !in solution.first) {
+                    inside = false
+
+                    solution = if (solved.isEmpty()) -1..-1 to -1  // avoid null checks..
+                    else solved.removeFirst()
+
+                    builder.append(l[i])
+                } else if (i !in solution.first) {
+                    builder.append(l[i])
+                }
+            }
+
+            l = builder.toString()
+        }
+
+        return solveGroup(l, precedence)
+    }
+
+    fun part1() = lines
+        .parallelStream()
+        .map { solveLine(it) }
+        .reduce { t, u -> t + u }
+        .get()
+
+    fun part2() = lines
+        .parallelStream()
+        .map { solveLine(it, precedence = true) }
+        .reduce { t, u -> t + u }
+        .get()
+}

2020/src/main/kotlin/Day19.kt

@@ -0,0 +1,57 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Groups
+import be.vandewalleh.aoc.utils.input.Input
+import java.util.*
+import kotlin.collections.ArrayList
+
+@Day(19)
+class Day19(@Groups val input: Input<List<List<String>>>) {
+    private val rules = input.value[0]
+    private val messages = input.value[1]
+
+    sealed class Rule {
+        data class CharRule(val value: Char) : Rule()
+        data class OrRule(val a: List<Int>, val b: List<Int>?) : Rule() {
+            val all get() = listOfNotNull(a, b)
+        }
+    }
+
+    private fun parseRules(): Map<Int, Rule> {
+        val parsedRules = mutableMapOf<Int, Rule>()
+        rules.forEach {
+            val parts = it.split(":", limit = 2)
+            val index = parts[0].toInt()
+            val rule = if ("\"" !in parts[1]) {
+                val p = parts[1].split('|', limit = 2).map { it.trim().split(" ").mapTo(ArrayList(2)) { it.toInt() } }
+                Rule.OrRule(p[0], if (p.size == 2) p[1] else null)
+            } else {
+                Rule.CharRule(parts[1].trim().replace("\"", "")[0])
+            }
+            parsedRules[index] = rule
+        }
+        return parsedRules
+    }
+
+    private fun matches(input: String, queue: ArrayDeque<Int>, rules: Map<Int, Rule>): Boolean =
+        if (queue.isEmpty()) input.isEmpty()
+        else if (input.isEmpty()) queue.isEmpty()
+        else when (val rule = rules[queue.pop()]!!) {
+            is Rule.CharRule -> input[0] == rule.value && matches(input.drop(1), queue, rules)
+            is Rule.OrRule -> rule.all.any { matches(input, queue.clone().apply { it.asReversed().forEach { addFirst(it) } }, rules) }
+        }
+
+    fun part1(): Int {
+        val rules = parseRules()
+        return messages.count { matches(it, ArrayDeque<Int>().apply { add(0) }, rules) }
+    }
+
+    fun part2(): Int {
+        val rules = parseRules().toMutableMap()
+        rules[8] = Rule.OrRule(listOf(42), listOf(42, 8))
+        rules[11] = Rule.OrRule(listOf(42, 31), listOf(42, 11, 31))
+        return messages.count { matches(it, ArrayDeque<Int>().apply { add(0) }, rules) }
+    }
+
+}

2020/src/main/kotlin/Day20.kt

@@ -0,0 +1,205 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.days.geometry.Grid
+import be.vandewalleh.aoc.days.geometry.gridOf
+import be.vandewalleh.aoc.days.geometry.transformations
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Groups
+import be.vandewalleh.aoc.utils.input.Input
+import java.util.*
+import kotlin.collections.ArrayList
+import kotlin.math.sqrt
+
+private typealias Tile = Grid<Char>
+
+@Day(20)
+class Day20(@Groups val input: Input<List<List<String>>>) {
+    private val tiles: Map<Int, Tile> = input.value
+        .map { it[0].let { it.substring(5 until it.indexOf(':')).toInt() } to it.drop(1) }
+        .associate { (id, tile) -> id to gridOf(tile) }
+
+    private fun Tile.allEdges() = listOf(edges(), edges().map { it.reversed() }).flatten()
+
+    private fun edgesMatch(a: Tile, b: Tile): Boolean {
+        val edges = b.allEdges()
+        return a.allEdges().any { a -> edges.any { a == it } }
+    }
+
+    private fun combine(tiles: List<Tile>) = sequence {
+        for (i in 0 until tiles.lastIndex) {
+            val a = tiles[i]
+            for (j in i + 1 until tiles.size) {
+                val b = tiles[j]
+                yield(a to b)
+            }
+        }
+    }
+
+    private fun tilesByNeighbourCount(): MutableMap<Int, MutableList<Tile>> {
+        val neighbours = combine(tiles.values.toList())
+            .filter { (a, b) -> edgesMatch(a, b) }
+            .map { it.toList() }
+            .flatten()
+            .groupBy { it }
+            .values
+
+        val map = mutableMapOf<Int, MutableList<Tile>>()
+        for (neighbour in neighbours) {
+            map.computeIfAbsent(neighbour.size) { mutableListOf() }.add(neighbour.first())
+        }
+        return map
+    }
+
+    fun part1() = tilesByNeighbourCount()[2]!!
+        .map { tile -> tiles.entries.find { it.value == tile }!!.key.toLong() }
+        .reduce { acc, id -> acc * id }
+
+    private fun neighboursCount(grid: Grid<*>, x: Int, y: Int): Int {
+        var neighboursCount = 2
+        if (x != 0 && x != grid.lastColumnIndex) neighboursCount++
+        if (y != 0 && y != grid.lastRowIndex) neighboursCount++
+        return neighboursCount
+    }
+
+    private fun isLeftOk(grid: Grid<Tile?>, x: Int, y: Int, candidate: Tile) = grid[x - 1, y]
+        ?.let { left -> candidate.firstColumn() == left.lastColumn() }
+        ?: true
+
+    private fun isTopOk(grid: Grid<Tile?>, x: Int, y: Int, candidate: Tile) = grid[x, y - 1]
+        ?.let { top -> candidate.firstRow() == top.lastRow() }
+        ?: true
+
+    private fun isBottomOk(grid: Grid<*>, x: Int, y: Int, candidate: Tile, neighbours: Map<Int, List<Tile>>) =
+        if (y == grid.lastRowIndex) true
+        else neighbours[neighboursCount(grid, x, y + 1)]!!
+            .filterNot { it == candidate }
+            .count { it.transformations().any { candidate.lastColumn() == it.firstColumn() } } == 1
+
+    private fun isRightOk(grid: Grid<*>, x: Int, y: Int, candidate: Tile, neighbours: Map<Int, List<Tile>>) =
+        if (x == grid.lastColumnIndex) true
+        else neighbours[neighboursCount(grid, x + 1, y)]!!
+            .filterNot { it == candidate }
+            .count { it.transformations().any { candidate.lastRow() == it.firstRow() } } == 1
+
+    private fun assembleGrid(): Grid<Tile?> {
+        val size = sqrt(tiles.size.toDouble()).toInt()
+        val grid: Grid<Tile?> = Grid(Array(size) { Array(size) { null } })
+
+        val neighbours: MutableMap<Int, MutableList<Tile>> = tilesByNeighbourCount()
+
+        for (y in 0 until grid.height) {
+            for (x in 0 until grid.width) {
+                val neighboursCount = neighboursCount(grid, x, y)
+                val candidates = neighbours[neighboursCount]!!
+
+                val conditions = mutableListOf<(Tile) -> Boolean>()
+                conditions += { isLeftOk(grid, x, y, it) }
+                conditions += { isTopOk(grid, x, y, it) }
+
+                // why is this condition needed ?
+                if (x == 0 && y == 0) {
+                    conditions += { isBottomOk(grid, x, y, it, neighbours) }
+                    conditions += { isRightOk(grid, x, y, it, neighbours) }
+                }
+
+                var found: Tile? = null
+
+                outer@ for (candidate in candidates) {
+                    for (transform in candidate.transformations()) {
+                        if (conditions.all { it(transform) }) {
+                            found = transform
+                            candidates.remove(candidate)
+                            break@outer
+                        }
+                    }
+                }
+
+                check(found != null)
+                grid[x, y] = found
+            }
+        }
+
+        return grid
+    }
+
+    private fun removeGaps(grid: Grid<Tile?>) {
+        for (y in 0 until grid.height) {
+            for (x in 0 until grid.width) {
+                grid[x, y] = removeGaps(grid[x, y]!!)
+            }
+        }
+    }
+
+    private fun removeGaps(tile: Tile): Tile {
+        val oldData: ArrayList<ArrayList<Char>> = tile.data
+        val newData = ArrayList<ArrayList<Char>>(oldData.size - 2)
+        oldData.subList(1, oldData.size - 1).forEach { d ->
+            val l = ArrayList<Char>().apply {
+                addAll(d.subList(1, d.size - 1))
+            }
+            newData.add(l)
+        }
+        return Tile(newData)
+    }
+
+    private fun gridToTile(grid: Grid<Tile?>): Tile {
+        val newData = ArrayList<ArrayList<Char>>()
+        for (y in 0 until grid.height) {
+            val row = grid.row(y)
+            for (yy in 0 until row[0]!!.height) {
+                val combinedRow = ArrayList<Char>().also { newData.add(it) }
+                row.forEach { combinedRow.addAll(it!!.row(yy)) }
+            }
+        }
+        return Tile(newData)
+    }
+
+    private fun Tile.subGridData(startX: Int, startY: Int, width: Int, height: Int): List<List<Char>> {
+        val newData = ArrayList<ArrayList<Char>>()
+        for (y in startY until startY + height) {
+            val row = ArrayList<Char>().also { newData.add(it) }
+            for (x in startX until startX + width) {
+                row.add(this[x, y]!!)
+            }
+        }
+        return newData
+    }
+
+    private fun List<List<Char>>.isMonster(monster: List<List<Char>>): Boolean {
+        val monsterRe = monster.joinToString("") { it.joinToString("") }.replace(" ", ".").toRegex()
+        val str = this.joinToString("") { it.joinToString("") }
+        return monsterRe.matches(str)
+    }
+
+    fun part2(): Int {
+        val grid = assembleGrid()
+        removeGaps(grid)
+        val megaTile = gridToTile(grid)
+
+        val monster: List<List<Char>> = """
+            |                  # |
+            |#    ##    ##    ###|
+            | #  #  #  #  #  #   |
+        """.trimMargin("|").lines().map { it.toCharArray().dropLast(1) }
+
+        val monsterWidth = monster[0].size
+        val monsterHeight = 3
+        val monsterSquares = monster.flatten().count { it == '#' }
+        val squares = megaTile.data.flatten().count { it == '#' }
+
+        for (g in megaTile.transformations()) {
+            var count = 0
+            for (y in 0 until g.lastRowIndex - monsterHeight) {
+                for (x in 0 until g.lastColumnIndex - monsterWidth) {
+                    val subgrid = g.subGridData(x, y, monsterWidth, monsterHeight)
+                    if (subgrid.isMonster(monster)) {
+                        count++
+                    }
+                }
+            }
+            if (count != 0) return squares - (count * monsterSquares)
+        }
+        error("No monsters found")
+    }
+
+}

2020/src/main/kotlin/Day21.kt

@@ -0,0 +1,58 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+import org.eclipse.collections.api.factory.Bags
+import org.eclipse.collections.api.multimap.set.MutableSetMultimap
+import org.eclipse.collections.impl.factory.Multimaps
+
+@Day(21)
+class Day21(@Lines val input: Input<List<String>>) {
+    private val foods = input.value.map { line ->
+        val parOpen = line.indexOf('(')
+        val ingredients = line.substring(0 until parOpen - 1).split(" ")
+        val allergens = line.substring(parOpen + 1 until line.length - 1).removePrefix("contains ").split(", ")
+        ingredients to allergens
+    }
+
+    private val allIngredients = foods.flatMap { it.first }.toSet()
+    private val allAllergens = foods.flatMap { it.second }.toSet()
+    private val dangerousIngredients = dangerousIngredients()
+
+    fun part1(): Int {
+        val occurrences = Bags.mutable.empty<String>()
+        foods.forEach { (ingredients) -> occurrences.addAll(ingredients) }
+        return allIngredients.filter { !dangerousIngredients.containsValue(it) }
+            .map { ingredient -> occurrences.count { it == ingredient } }
+            .sum()
+    }
+
+    fun part2(): String {
+        while (!dangerousIngredients.multiValuesView().all { it.size() == 1 }) {
+            dangerousIngredients.multiValuesView()
+                .filter { it.size() == 1 }
+                .map { it.first() }
+                .forEach { removeMe ->
+                    dangerousIngredients.keyMultiValuePairsView()
+                        .filter { it.two.size() != 1 && it.two.contains(removeMe) }
+                        .forEach { dangerousIngredients.remove(it.one, removeMe) }
+                }
+        }
+        return dangerousIngredients.keySet().sorted().joinToString(",") { dangerousIngredients.get(it).first() }
+    }
+
+    private fun dangerousIngredients(): MutableSetMultimap<String, String> {
+        val map = Multimaps.mutable.set.empty<String, String>()
+        allAllergens.forEach { map.putAll(it, allIngredients) }
+
+        foods.forEach { (ingredients, allergens) ->
+            allergens.forEach { allergen ->
+                allIngredients.forEach {
+                    if (!ingredients.contains(it)) map.remove(allergen, it)
+                }
+            }
+        }
+        return map
+    }
+}

2020/src/main/kotlin/Day22.kt

@@ -0,0 +1,77 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Groups
+import be.vandewalleh.aoc.utils.input.Input
+
+private data class PlayedGame(val a: List<Int>, val b: List<Int>)
+
+@Day(22)
+class Day22(@Groups val input: Input<List<List<String>>>) {
+    private val one = input.value[0].drop(1).map { it.toInt() }
+    private val two = input.value[1].drop(1).map { it.toInt() }
+
+    fun part1(): Long {
+        val oneDeque = ArrayDeque(one)
+        val twoDeque = ArrayDeque(two)
+
+        while (oneDeque.isNotEmpty() && twoDeque.isNotEmpty()) {
+            val a = oneDeque.removeFirst()
+            val b = twoDeque.removeFirst()
+
+            if (a > b) {
+                oneDeque.addLast(a)
+                oneDeque.addLast(b)
+            } else {
+                twoDeque.addLast(b)
+                twoDeque.addLast(a)
+            }
+        }
+
+        val deque = if (oneDeque.isEmpty()) twoDeque else oneDeque
+        return deque.score()
+    }
+
+    private fun ArrayDeque<Int>.score() =
+        asReversed().mapIndexed { index, value -> (index + 1).toLong() * value.toLong() }.sum()
+
+    fun part2(): Long {
+        val oneDeque = ArrayDeque(one)
+        val twoDeque = ArrayDeque(two)
+
+        val winner = playGame(oneDeque, twoDeque)
+        val deque = if (winner == 1) oneDeque else twoDeque
+        return deque.score()
+    }
+
+    private fun playGame(one: ArrayDeque<Int>, two: ArrayDeque<Int>): Int {
+        val playedGames = mutableSetOf<PlayedGame>()
+
+        while (one.isNotEmpty() && two.isNotEmpty()) {
+            if (!playedGames.add(PlayedGame(one.toList(), two.toList()))) return 1
+
+            val a = one.removeFirst()
+            val b = two.removeFirst()
+
+            val winner = when {
+                one.size >= a && two.size >= b -> playGame(
+                    ArrayDeque(one.take(a)),
+                    ArrayDeque(two.take(b))
+                )
+                a > b -> 1
+                else -> 2
+            }
+
+            if (winner == 1) {
+                one.addLast(a)
+                one.addLast(b)
+            } else {
+                two.addLast(b)
+                two.addLast(a)
+            }
+
+        }
+
+        return if (one.isEmpty()) 2 else 1
+    }
+}

2020/src/main/kotlin/Day23.kt

@@ -0,0 +1,112 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Text
+
+@Day(23)
+class Day23(@Text val input: Input<String>) {
+    private val cups = input.value.toCharArray().map { it.toString().toInt() }
+
+    private fun <T> ringSequence(head: Ring.Node<T>) = generateSequence(head) { it.next }
+
+    class Ring<T>(items: Iterable<T>) {
+
+        class Node<T>(var value: T) {
+            lateinit var next: Node<T>
+            override fun toString() = "Node($value -> ${next.value})"
+        }
+
+        private var last: Node<T>? = null
+        private var first: Node<T>? = null
+
+        init {
+            items.forEach { item ->
+                val node = Node(item)
+                if (first == null) first = node
+                last?.next = node
+                last = node
+            }
+            check(first != null && last != null)
+            last?.next = first!!
+        }
+
+        fun first() = first!!
+    }
+
+    private fun Ring.Node<Int>.cached(size: Int): Array<Ring.Node<Int>> =
+        arrayOfNulls<Ring.Node<Int>>(size + 1).also { array ->
+            array[0] = Ring.Node(-1)
+            ringSequence(this).take(size).forEach { array[it.value] = it }
+        } as Array<Ring.Node<Int>>
+
+    fun part1(): String {
+        var currentNode = Ring(cups).first()
+        val cache = currentNode.cached(cups.size)
+        val max = cups.maxOrNull()!!
+
+        repeat(100) { currentNode = move(max, cache, currentNode) }
+
+        return ringSequence(currentNode)
+            .dropWhile { it.value != 1 }
+            .drop(1)
+            .take(cups.size - 1)
+            .map { it.value }
+            .joinToString("")
+    }
+
+    fun part2(): Long {
+        fun fillCups(): List<Int> {
+            val cups = ArrayList<Int>(1_000_000)
+            cups.addAll(this.cups)
+            val highest = this.cups.maxOrNull()!!
+
+            for (i in 1..1_000_000 - cups.size) {
+                cups.add(highest + i)
+            }
+
+            return cups
+        }
+
+        val size = 1_000_000
+        var currentNode = Ring(fillCups()).first()
+        val cache = currentNode.cached(size)
+
+        repeat(10_000_000) { currentNode = move(max = size, cache, currentNode) }
+
+        val one = cache[1]
+        val a = one.next
+        val b = a.next
+        return a.value.toLong() * b.value.toLong()
+    }
+
+    private fun move(max: Int, cache: Array<Ring.Node<Int>>, current: Ring.Node<Int>): Ring.Node<Int> {
+        val a = current.next
+        val b = a.next
+        val c = b.next
+
+        current.next = c.next
+
+        val aa = a.value
+        val bb = b.value
+        val cc = c.value
+
+        val destinationNode: Ring.Node<Int>
+        var i = current.value - 1
+        while (true) {
+            if (i < 1) i = max
+            val value = cache[i].value
+            if (value == aa || value == bb || value == cc) {
+                i--
+            } else {
+                destinationNode = cache[i]
+                break
+            }
+        }
+
+        val destinationNextNode = destinationNode.next
+        destinationNode.next = a
+        c.next = destinationNextNode
+        return current.next
+    }
+}

2020/src/main/kotlin/Day24.kt

@@ -0,0 +1,66 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+import org.eclipse.collections.api.bag.Bag
+import org.eclipse.collections.api.bag.MutableBag
+import org.eclipse.collections.api.factory.Bags
+
+@Day(24)
+class Day24(@Lines val input: Input<List<String>>) {
+
+    private data class HexPoint(val x: Int, val y: Int, val z: Int) {
+        fun translate(other: HexPoint) = HexPoint(this.x + other.x, this.y + other.y, this.z + other.z)
+    }
+
+    private enum class Direction(vararg coordinates: Int) {
+        E(1, -1, 0),
+        SE(0, -1, 1),
+        SW(-1, 0, 1),
+        W(-1, 1, 0),
+        NW(0, 1, -1),
+        NE(1, 0, -1);
+
+        val coordinates = HexPoint(coordinates[0], coordinates[1], coordinates[2])
+    }
+
+    private fun parseTile(line: String) = "e|se|sw|w|nw|ne".toRegex()
+        .findAll(line)
+        .flatMap { it.groupValues }
+        .map { Direction.valueOf(it.toUpperCase()) }
+        .toList()
+
+    private val tiles = input.value.map { parseTile(it) }.map {
+        it.map { it.coordinates }.reduce { acc, ints -> acc.translate(ints) }
+    }
+
+    fun part1() = Bags.immutable.ofAll(tiles).selectBlacks().size()
+
+    private fun Bag<HexPoint>.selectBlacks() = selectByOccurrences { it % 2 == 1 }
+
+    private fun HexPoint.adjacents() = Direction.values().map { this.translate(it.coordinates) }
+
+    // black -> odd
+    // white -> even || not in bag -> !in black
+    private fun day(bag: MutableBag<HexPoint>) {
+        val blacks = bag.selectBlacks().toSet()
+
+        val all = (bag + bag.flatMap { it.adjacents() }).toSet()
+
+        for (tile in all) {
+            val adjacents = tile.adjacents()
+            val adjacentBlacks = adjacents.count { it in blacks }
+            val isBlack = tile in blacks
+
+            if (isBlack && (adjacentBlacks == 0 || adjacentBlacks > 2)) bag.setOccurrences(tile, 2)
+            else if (!isBlack && adjacentBlacks == 2) bag.setOccurrences(tile, 1)
+        }
+    }
+
+    fun part2(): Int {
+        val bag = Bags.mutable.ofAll(tiles)
+        repeat(100) { day(bag) }
+        return bag.selectBlacks().size()
+    }
+}

2020/src/main/kotlin/Day25.kt

@@ -0,0 +1,45 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+
+@Day(25)
+class Day25(@Lines val input: Input<IntArray>) {
+    private val doorPublicKey = input.value[0]
+    private val cardPublicKey = input.value[1]
+
+    private fun encryptionKey(loopSize: Int, publicKey: Int) = transformSubjectNumber(loopSize, publicKey)
+
+    private fun transformSubjectNumber(loopSize: Int, subjectNumber: Int): Int {
+        var number = 1L
+        repeat(loopSize) {
+            number *= subjectNumber
+            number %= 20201227
+        }
+        return number.toInt()
+    }
+
+    private fun transformSubjectNumberStartingWith(currentNumber: Long, subjectNumber: Int): Long {
+        var number = currentNumber
+        number *= subjectNumber
+        number %= 20201227
+        return number
+    }
+
+    private fun findLoopSize(expectedPublicKey: Long): Int {
+        var computedPublicKey = 1L
+        var loopSize = 0
+        do {
+            computedPublicKey = transformSubjectNumberStartingWith(computedPublicKey, 7)
+            loopSize++
+        } while (computedPublicKey != expectedPublicKey)
+        return loopSize
+    }
+
+    fun part1(): Int {
+        val cardLoopSize = findLoopSize(cardPublicKey.toLong())
+        return encryptionKey(cardLoopSize, doorPublicKey)
+    }
+
+}

2020/src/main/kotlin/Main.kt

@@ -0,0 +1,7 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.factory.createDay
+
+fun main() = with(createDay<Day25>()) {
+    println(part1())
+}

2020/src/main/kotlin/geometry/Grid.kt

@@ -0,0 +1,64 @@
+@file:Suppress("MemberVisibilityCanBePrivate")
+
+package be.vandewalleh.aoc.days.geometry
+
+class Grid<T> {
+    val data: ArrayList<ArrayList<T>> = ArrayList()
+
+    constructor(data: Iterable<Iterable<T>>) {
+        data.forEach {
+            this.data.add(ArrayList(it.toList()))
+        }
+    }
+
+    constructor(data: Array<Array<T>>) {
+        data.forEach {
+            this.data.add(ArrayList(it.toList()))
+        }
+    }
+
+    val width get() = data[0].size
+    val lastColumnIndex get() = data[0].size - 1
+
+    val height get() = data.size
+    val lastRowIndex get() = data.size - 1
+
+    operator fun get(x: Int, y: Int): T? {
+        if (y !in 0..lastRowIndex) return null
+        val row = data[y]
+        return if (x !in 0..lastColumnIndex) null
+        else row[x]
+    }
+
+    operator fun set(x: Int, y: Int, value: T) {
+        data[y][x] = value
+    }
+
+    fun row(y: Int): List<T> = data[y]
+    fun firstRow() = row(0)
+    fun lastRow() = row(height - 1)
+
+    fun column(x: Int): List<T> = data.map { it[x] }
+    fun firstColumn() = column(0)
+    fun lastColumn() = column(width - 1)
+
+    fun edges() = listOf(row(0), column(0), row(lastRowIndex), column(lastColumnIndex))
+
+    override fun toString() = buildString {
+        data.forEach { line ->
+            append(line.joinToString(""))
+            appendLine()
+        }
+    }
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (javaClass != other?.javaClass) return false
+        other as Grid<*>
+        if (data != other.data) return false
+        return true
+    }
+
+    override fun hashCode() = data.hashCode()
+
+}

2020/src/main/kotlin/geometry/GridFactory.kt

@@ -0,0 +1,7 @@
+package be.vandewalleh.aoc.days.geometry
+
+fun gridOf(lines: List<String>): Grid<Char> =
+    Grid(lines.map { it.toCharArray().toList() })
+
+fun gridOf(lines: String): Grid<Char> =
+    gridOf(lines.lines())

2020/src/main/kotlin/geometry/GridTranformations.kt

@@ -0,0 +1,53 @@
+package be.vandewalleh.aoc.days.geometry
+
+import java.util.*
+
+private fun <T> ArrayList<T>.reversed(): ArrayList<T> {
+    val out = ArrayList<T>(this.size)
+    asReversed().forEach { out.add(it) }
+    return out
+}
+
+fun <T> Grid<T>.flipVertically(): Grid<T> = Grid(data.reversed())
+
+fun <T> Grid<T>.flipHorizontally(): Grid<T> {
+    val out = ArrayList<ArrayList<T>>(height)
+    for (y in 0 until height) {
+        out.add(data[y].reversed())
+    }
+    return Grid(out)
+}
+
+fun <T> Grid<T>.rotateRight(): Grid<T> {
+    val out = ArrayList<ArrayList<T>>(width)
+    for (x in 0 until width) {
+        out.add(ArrayList<T>(height))
+        for (y in 0 until height) {
+            out[x].add(data[y][x])
+        }
+    }
+    return Grid(out).flipHorizontally()
+}
+
+fun <T> Grid<T>.rotateLeft(): Grid<T> {
+    val data = flipHorizontally().data
+    val out = ArrayList<ArrayList<T>>(width)
+    for (x in 0 until width) {
+        out.add(ArrayList<T>(height))
+        for (y in 0 until height) {
+            out[x].add(data[y][x])
+        }
+    }
+    return Grid(out).flipHorizontally()
+}
+
+fun <T> Grid<T>.transformations(): Sequence<Grid<T>> = sequence {
+    yield(this@transformations)
+    yield(flipHorizontally())
+    yield(flipVertically())
+    yield(rotateLeft())
+    yield(rotateRight())
+    yield(flipHorizontally().flipVertically())
+    yield(flipVertically().rotateRight())
+    yield(flipVertically().rotateLeft())
+}