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Day 11 Part 2

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Sven Weidauer 2024-12-12 18:56:24 +01:00
parent 9e8f49963c
commit 0aa30cca2a
1 changed files with 16 additions and 19 deletions
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35
2024/src/main/kotlin/day11.kt
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@ -1,31 +1,28 @@
fun main() { fun main() {
val input = readInputString("day11.txt").split(" ").map { it.toLong() } val input = readInputString("day11.txt").split(" ").map { it.toLong() }
val part1 = (1..25).fold(input) { result, _ -> val part1 = input.blink(25)
result.blink()
}.count()
println("Part 1: $part1") println("Part 1: $part1")
val part2 = input.blink(75)
val part2 = (1..75).fold(input) { result, _ ->
result.blink()
}.count()
println("Part 2: $part2") println("Part 2: $part2")
} }
fun List<Long>.blink() = flatMap { fun List<Long>.blink(count: Int) = fold(0L) { acc, stone -> acc + blink(stone, count) }
val str = "$it"
val memo = mutableMapOf<Pair<Long, Int>, Long>()
fun blink(stone: Long, count: Int): Long = memo.getOrPut(Pair(stone, count)) {
if (count == 0) return 1
val str = "$stone"
val strLen = str.count() val strLen = str.count()
when { when {
it == 0L -> listOf(1L) stone == 0L -> blink(1L, count - 1)
strLen % 2 == 0 -> listOf( strLen % 2 == 0 ->
str.substring(0, strLen / 2).toLong(), blink(str.substring(0, strLen / 2).toLong(), count - 1) +
str.substring(strLen / 2).toLong() blink(str.substring(strLen / 2).toLong(), count - 1)
)
else -> listOf(it * 2024) else -> blink(stone * 2024, count - 1)
} }
} }