Move year 2021 into a subfolder

1 files changed, 46 insertions, 0 deletions

diff --git a/2021-kotlin/src/Day14.kt b/2021-kotlin/src/Day14.kt
new file mode 100644
index 0000000..920ea9e
--- /dev/null
+++ b/2021-kotlin/src/Day14.kt
@@ -0,0 +1,46 @@
+object Day14 {
+    private 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 part1(input: List<String>): Long = getPolymerLetterCounts(input, 10)
+
+    fun part2(input: List<String>): Long = getPolymerLetterCounts(input, 40)
+}
+
+fun main() {
+    val testInput = readInputAsLines("Day14_test")
+    check(Day14.part1(testInput) == 1588L)
+    check(Day14.part2(testInput) == 2188189693529L)
+
+    val input = readInputAsLines("Day14")
+    println(Day14.part1(input))
+    println(Day14.part2(input))
+}