1 files changed, 58 insertions, 0 deletions
diff --git a/src/Day06.kt b/src/Day06.kt
new file mode 100644
index 0000000..d192c72
--- /dev/null
+++ b/src/Day06.kt
@@ -0,0 +1,58 @@
+fun main() {
+    fun part1(input: String): Int {
+        var fish = input.trim().split(",").map(String::toInt)
+
+        repeat(80) {
+            val pendingFish = mutableListOf<Int>()
+
+            fish = fish.map {
+                when (it) {
+                    0 -> {
+                        pendingFish.add(8)
+                        6
+                    }
+                    else -> {
+                        it - 1
+                    }
+                }
+            } + pendingFish
+        }
+
+        return fish.size
+    }
+
+    fun part2(input: String): Long {
+        val fishCounts =
+            input
+                .trim()
+                .split(",")
+                .map(String::toInt)
+                .groupingBy { it }
+                .eachCount()
+                .mapValues { (_, v) -> v.toLong() }
+                .toMutableMap()
+
+        repeat(256) {
+            val readyToBirth = fishCounts.getOrDefault(0, 0)
+            fishCounts[0] = fishCounts.getOrDefault(1, 0)
+            fishCounts[1] = fishCounts.getOrDefault(2, 0)
+            fishCounts[2] = fishCounts.getOrDefault(3, 0)
+            fishCounts[3] = fishCounts.getOrDefault(4, 0)
+            fishCounts[4] = fishCounts.getOrDefault(5, 0)
+            fishCounts[5] = fishCounts.getOrDefault(6, 0)
+            fishCounts[6] = fishCounts.getOrDefault(7, 0) + readyToBirth
+            fishCounts[7] = fishCounts.getOrDefault(8, 0)
+            fishCounts[8] = readyToBirth
+        }
+
+        return fishCounts.values.sum()
+    }
+
+    val testInput = readInputAsString("Day06_test")
+    check(part1(testInput) == 5934)
+    check(part2(testInput) == 26984457539)
+
+    val input = readInputAsString("Day06")
+    println(part1(input))
+    println(part2(input))
+}