1 files changed, 45 insertions, 0 deletions
diff --git a/src/Day14.kt b/src/Day14.kt
new file mode 100644
index 0000000..fb6a43e
--- /dev/null
+++ b/src/Day14.kt
@@ -0,0 +1,45 @@
+fun getPolymerLetterCounts(input: List<String>, iterations: Int): Long {
+    val template = input.first()
+    val rules = input.drop(2).associate {
+        val (pattern, replacement) = it.split(" -> ")
+        (pattern[0] to pattern[1]) to replacement.first()
+    }
+
+    var pairCounts = template
+        .zipWithNext()
+        .groupingBy { it }
+        .eachCount()
+        .mapValues { (_, v) -> v.toLong() }
+
+    repeat(iterations) {
+        val newCounts = mutableMapOf<Pair<Char, Char>, Long>()
+
+        pairCounts.forEach { (pair, count) ->
+            newCounts.merge(rules[pair]!! to pair.second, count, Long::plus)
+            newCounts.merge(pair.first to rules[pair]!!, count, Long::plus)
+        }
+
+        pairCounts = newCounts
+    }
+
+    val letterCounts = mutableMapOf<Char, Long>()
+    pairCounts.forEach { (pair, count) -> letterCounts.merge(pair.second, count, Long::plus) }
+    letterCounts.merge(template.first(), 1, Long::plus)
+
+    return letterCounts.values.let { it.maxOrNull()!! - it.minOrNull()!! }
+}
+
+fun main() {
+    fun part1(input: List<String>): Long = getPolymerLetterCounts(input, 10)
+
+    fun part2(input: List<String>): Long = getPolymerLetterCounts(input, 40)
+
+
+    val testInput = readInputAsLines("Day14_test")
+    check(part1(testInput) == 1588L)
+    check(part2(testInput) == 2188189693529L)
+
+    val input = readInputAsLines("Day14")
+    println(part1(input))
+    println(part2(input))
+}