Day14 2021

2021/src/main/kotlin/Day14.kt

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+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.BaseDay
+import be.vandewalleh.aoc.utils.input.Day
+
+@Day
+class Day14 : BaseDay() {
+
+    private fun run(step: Int): Long {
+        val template = input.lines.value.first()
+        // {CH=(CB, BH), NN=(NC, CN), ...}
+        val pairs = input.lines.value.drop(2)
+            .associate { it.split(" -> ").let { (a, b) -> a to (a[0] + b to b + a[1]) } }
+
+        fun <K> Map<K, Int>.toLong() = mapValues { it.value.toLong() }.toMutableMap()
+
+        // {NN=1, NC=1, CB=1}
+        val polymer = template.windowed(2).groupingBy { it }.eachCount().toLong()
+
+        // {N=2, C=1, ...}
+        val counts = template.groupingBy { it }.eachCount().toLong()
+        repeat(step) {
+            polymer.toMap().forEach { (pair, value) ->
+                val (left, right) = pairs[pair]!!
+                polymer[pair]?.let { old -> polymer[pair] = old - value }
+                polymer[left] = (polymer[left] ?: 0) + value
+                polymer[right] = (polymer[right] ?: 0) + value
+                counts[left[1]] = (counts[left[1]] ?: 0) + value
+            }
+        }
+        return counts.maxOf { it.value } - counts.minOf { it.value }
+    }
+
+    override fun part1() = run(10)
+    override fun part2() = run(40)
+}

2021/src/main/resources/day14.txt

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+PHVCVBFHCVPFKBNHKNBO
+
+HK -> F
+VN -> S
+NB -> F
+HF -> B
+CK -> N
+VP -> B
+HO -> P
+NH -> N
+CC -> N
+FC -> P
+OK -> S
+OO -> P
+ON -> C
+VF -> B
+NN -> O
+KS -> P
+FK -> K
+HB -> V
+SH -> O
+OB -> K
+PB -> V
+BO -> O
+NV -> K
+CV -> H
+PH -> H
+KO -> B
+BC -> B
+KC -> B
+SO -> P
+CF -> V
+VS -> F
+OV -> N
+NS -> K
+KV -> O
+OP -> O
+HH -> C
+FB -> S
+CO -> K
+SB -> K
+SN -> V
+OF -> F
+BN -> F
+CP -> C
+NC -> H
+VH -> S
+HV -> V
+NF -> B
+SS -> K
+FO -> F
+VO -> H
+KK -> C
+PF -> V
+OS -> F
+OC -> H
+SK -> V
+FF -> H
+PK -> N
+PC -> O
+SP -> B
+CB -> B
+CH -> H
+FN -> V
+SV -> O
+SC -> P
+NP -> B
+BB -> S
+PV -> S
+VB -> P
+SF -> H
+VC -> O
+HN -> V
+BF -> O
+NO -> O
+HP -> N
+VV -> K
+HS -> P
+FH -> N
+KB -> F
+KF -> B
+PN -> K
+KH -> K
+CN -> S
+PP -> O
+BP -> O
+OH -> B
+FS -> O
+BK -> B
+PO -> V
+CS -> C
+BV -> N
+KP -> O
+KN -> B
+VK -> F
+HC -> O
+BH -> B
+FP -> H
+NK -> V
+BS -> C
+FV -> F
+PS -> P

2021/src/test/kotlin/Day14Test.kt

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+package be.vandewalleh.aoc.days
+
+class Day14Test : BaseDayTest() {
+    override val example = """
+        NNCB
+
+        CH -> B
+        HH -> N
+        CB -> H
+        NH -> C
+        HB -> C
+        HC -> B
+        HN -> C
+        NN -> C
+        BH -> H
+        NC -> B
+        NB -> B
+        BN -> B
+        BB -> N
+        BC -> B
+        CC -> N
+        CN -> C
+    """.trimIndent()
+
+    override val part1Example = 1588L
+    override val part1Answer = 3555L
+
+    override val part2Example = 2188189693529
+    override val part2Answer = 4439442043739
+}