Day20 part1

days/src/main/kotlin/Day20.kt

@@ -0,0 +1,80 @@
+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 be.vandewalleh.aoc.utils.input.createDay
+
+private typealias Tile = Array<CharArray>
+
+@Day(20)
+class Day20(@Groups val input: Input<List<List<String>>>) {
+
+    private val tiles = input.value
+        .map { it[0].let { it.substring(5 until it.indexOf(':')).toInt() } to it.drop(1) }
+        .map { (id, tile) -> id to tile.map { it.toCharArray() }.toTypedArray() }
+
+    private fun Tile.sides() = sequence {
+        val tile = this@sides
+        yield(tile[0])
+        yield(tile[tile.lastIndex])
+        yield(tile[0].reversedArray())
+        yield(tile[tile.lastIndex].reversedArray())
+        yield(tile.map { it[0] }.toCharArray())
+        yield(tile.map { it[tile.lastIndex] }.toCharArray())
+        yield(tile.map { it[0] }.asReversed().toCharArray())
+        yield(tile.map { it[tile.lastIndex] }.asReversed().toCharArray())
+    }
+
+    private fun sideMatches(a: Tile, b: Tile): Boolean {
+        val aSides = a.sides()
+        val bSides = b.sides().toList()
+        aSides.forEach { aSide ->
+            bSides.forEach { bSide ->
+                if (aSide contentEquals bSide) return true
+            }
+        }
+        return false
+    }
+
+    private fun Tile.prettyPrint() {
+        val str = buildString {
+            this@prettyPrint.forEach { line ->
+                append(line.joinToString(""))
+                appendLine()
+            }
+        }
+        print(str)
+    }
+
+    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)
+            }
+        }
+    }
+
+    fun part1() = combine(tiles.map { it.second })
+        .filter { (a, b) -> sideMatches(a, b) }
+        .map { it.toList() }
+        .flatten()
+        .groupBy { it.map { it.toList() } }
+        .values
+        .asSequence()
+        .filter { it.size == 2 }
+        .flatten()
+        .toSet()
+        .map { tile -> tiles.find { it.second === tile }!! }
+        .map { it.first.toLong() }
+        .reduce { acc, id -> acc * id }
+}
+
+fun main() {
+    with(createDay<Day20>(
+    )) {
+        println(part1())
+    }
+}