aoc-2024 - Day11

Author: Krystian Kaniowski

advent-of-code-2024/src/Day11.kt

@@ -0,0 +1,54 @@
+import java.math.BigInteger
+
+// https://adventofcode.com/2024/day/11
+
+fun main() {
+
+
+ data class Cache(private val cache: MutableMap<Pair<Long, Int>, BigInteger> = mutableMapOf()) {
+ fun getCache(number: Long, deep: Int): BigInteger? = cache[number to deep]
+ fun saveCache(number: Long, deep: Int, result: BigInteger) {
+ cache[number to deep] = result
+ }
+ }
+
+ fun dig(cache: Cache, maxLevel: Int, level: Int, number: Long): BigInteger {
+ val cachedResult = cache.getCache(number, maxLevel - level)
+ return when {
+ level == maxLevel -> 1.toBigInteger()
+ cachedResult != null -> cachedResult
+ number == 0.toLong() -> dig(cache, maxLevel, level + 1, 1)
+ number.toString().length % 2 == 1 -> dig(cache, maxLevel, level + 1, number * 2024)
+ else -> {
+ val (n1, n2) = number.toString()
+ .let {
+ it.substring(0, it.length / 2).toLong() to it.substring(it.length / 2).toLong()
+ }
+ dig(cache, maxLevel, level + 1, n1) + dig(cache, maxLevel, level + 1, n2)
+ }
+ }.apply {
+ cache.saveCache(number, maxLevel - level, this)
+ }
+ }
+
+ fun part1(input: List<String>): BigInteger {
+ return input.first()
+ .split(" ")
+ .map { it.toLong() }
+ .sumOf { dig(Cache(), 25, 0, it) }
+ }
+
+ fun part2(input: List<String>): BigInteger {
+ return input.first()
+ .split(" ")
+ .map { it.toLong() }
+ .sumOf { dig(Cache(), 75, 0, it) }
+ }
+
+ val testInput = readInput("Day11_test")
+ val input = readInput("Day11")
+
+ testBigInteger(55312.toBigInteger()) { part1(testInput) }
+ execBigInteger { part1(input) }
+ execBigInteger { part2(input) }
+}