From 34c2414304d59e76d52b96efe6bebebb4e75f086 Mon Sep 17 00:00:00 2001
From: tchojnacki <tomaszchojnacki2001@gmail.com>
Date: Thu, 11 Aug 2022 12:01:44 +0200
Subject: Move year 2021 into a subfolder

---
 2021-kotlin/src/Day11.kt | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)
 create mode 100644 2021-kotlin/src/Day11.kt

(limited to '2021-kotlin/src/Day11.kt')

diff --git a/2021-kotlin/src/Day11.kt b/2021-kotlin/src/Day11.kt
new file mode 100644
index 0000000..db56d61
--- /dev/null
+++ b/2021-kotlin/src/Day11.kt
@@ -0,0 +1,48 @@
+object Day11 {
+    private 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 bothParts(input: List<String>) = flashSequence(parseToMap(input)).let { seq ->
+        seq.take(100).sum() to seq.indexOfFirst { it == 100 } + 1
+    }
+}
+
+fun main() {
+    val testInput = readInputAsLines("Day11_test")
+    val testOutput = Day11.bothParts(testInput)
+    check(testOutput.first == 1656)
+    check(testOutput.second == 195)
+
+    val input = readInputAsLines("Day11")
+    val output = Day11.bothParts(input)
+    println(output.first)
+    println(output.second)
+}
-- 
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