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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))
}
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