Day11 2021

2021/src/main/kotlin/Day11.kt

@@ -0,0 +1,63 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.BaseDay
+import be.vandewalleh.aoc.utils.input.Day
+
+@Day
+class Day11 : BaseDay() {
+
+    private data class Point(val x: Int, val y: Int) {
+        fun adjacents() = listOf(
+            copy(y = y - 1),
+            copy(x = x + 1),
+            copy(y = y + 1),
+            copy(x = x - 1),
+            copy(y = y - 1, x = x - 1),
+            copy(x = x + 1, y = y + 1),
+            copy(y = y + 1, x = x - 1),
+            copy(x = x + 1, y = y - 1),
+        )
+    }
+
+    private val map by lazy {
+        input.lines.value.flatMapIndexed { y, line ->
+            line.mapIndexed { x, value -> Point(x, y) to value.digitToInt() }
+        }.toMap()
+    }
+
+    override fun part1(): Int {
+        val map = map.toMap(HashMap())
+        var count = 0
+        repeat(100) { count += step(map) }
+        return count
+    }
+
+    private fun step(map: HashMap<Point, Int>): Int {
+        map.keys.forEach { map[it] = map[it]!! + 1 }
+        val flashed = hashSetOf<Point>()
+        while (true) {
+            val new = map.entries.asSequence()
+                .filter { it.value > 9 }
+                .filter { it.key !in flashed }
+                .onEach { flashed += it.key }
+                .flatMap { it.key.adjacents() }
+                .filter { it in map }
+                .toList()
+
+            if (new.isEmpty()) break
+            new.forEach { map[it] = map[it]!! + 1 }
+        }
+
+        map.entries.filter { it.value > 9 }
+            .map { it.key }
+            .forEach { map[it] = 0 }
+
+        return flashed.size
+    }
+
+    override fun part2(): Int {
+        val map = map.toMap(HashMap())
+        repeat(10000) { if (step(map) == map.size) return it + 1 }
+        return -1
+    }
+}

2021/src/main/resources/day11.txt

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+7222221271
+6463754232
+3373484684
+4674461265
+1187834788
+1175316351
+8211411846
+4657828333
+5286325337
+5771324832

2021/src/test/kotlin/Day11Test.kt

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+package be.vandewalleh.aoc.days
+
+class Day11Test : BaseDayTest(11) {
+    override val example = """
+        5483143223
+        2745854711
+        5264556173
+        6141336146
+        6357385478
+        4167524645
+        2176841721
+        6882881134
+        4846848554
+        5283751526
+    """.trimIndent()
+
+    override val part1Example = 1656
+    override val part1Answer = 1661
+
+    override val part2Example = 195
+    override val part2Answer = 334
+}