Day11

2020-12-11 08:06:45 +01:00
parent 34259208d5
commit b7ba2d10a7
2 changed files with 216 additions and 0 deletions
@@ -0,0 +1,123 @@
+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 be.vandewalleh.aoc.utils.input.createDay
+
+typealias Seats = Array<CharArray>
+
+fun Seats.deepClone(): Seats = map { it.clone() }.toTypedArray()
+
+operator fun Seats.get(x: Int, y: Int): Char = this[y][x]
+operator fun Seats.set(x: Int, y: Int, value: Char) {
+    this[y][x] = value
+}
+
+operator fun Seats.contains(xy: Pair<Int, Int>): Boolean {
+    val (x, y) = xy
+    return x in 0 until width && y in 0 until height
+}
+
+val Seats.width get() = first().size
+val Seats.height get() = size
+
+fun Seats.asGridString() = joinToString("\n") { it.joinToString("") }
+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()
+
+}
+
+fun main() = with(createDay<Day11>()) {
+    println(part1())
+    println(part2())
+}