1 files changed, 50 insertions, 0 deletions
diff --git a/src/Day11.kt b/src/Day11.kt
new file mode 100644
index 0000000..9a15344
--- /dev/null
+++ b/src/Day11.kt
@@ -0,0 +1,50 @@
+fun flashSequence(input: Map<Pos2D, Int>) = sequence {
+    val map = input.toMutableMap()
+
+    while (true) {
+        val flashed = mutableSetOf<Pos2D>()
+        fun canFlash(entry: Map.Entry<Pos2D, Int>): Boolean = entry.value > 9 && !flashed.contains(entry.key)
+
+        // 1)
+        map.forEach { (pos, energy) -> map[pos] = energy + 1 }
+
+        // 2)
+        while (map.any(::canFlash)) {
+            map
+                .filter(::canFlash)
+                .forEach { (pos, _) ->
+                    flashed.add(pos)
+                    Pos2D.directions8.map { pos + it }.forEach {
+                        if (map.containsKey(it)) {
+                            map[it] = map[it]!! + 1
+                        }
+                    }
+                }
+        }
+
+        // 3)
+        flashed.forEach { map[it] = 0 }
+
+        yield(flashed.size)
+    }
+}
+
+fun main() {
+    fun part1(input: List<String>): Int =
+        flashSequence(parseToMap(input))
+            .take(100)
+            .sum()
+
+    fun part2(input: List<String>): Int =
+        flashSequence(parseToMap(input))
+            .indexOfFirst { it == 100 } + 1
+
+
+    val testInput = readInputAsLines("Day11_test")
+    check(part1(testInput) == 1656)
+    check(part2(testInput) == 195)
+
+    val input = readInputAsLines("Day11")
+    println(part1(input))
+    println(part2(input))
+}