2024 Day 11, WIP...

src/main/kotlin/aoc/years/year2024/Day11.kt

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+package aoc.years.year2024
+
+import aoc.Day
+import java.math.BigInteger
+
+@Year2024
+class Day11 : Day() {
+
+    override fun solvePart1(input: List<String>): Any {
+        val memoization = HashMap<BigInteger, BigInteger>()
+        return getStones(input).sumOf { it.getNrOfStonesAfter(25, memoization) }
+    }
+
+    override fun solvePart2(input: List<String>): Any {
+        // try recursive with memoization?
+        val memoization = HashMap<BigInteger, BigInteger>()
+        return getStones(input).sumOf { it.getNrOfStonesAfter(25, memoization) }
+    }
+
+    private fun getStones(input: List<String>) = input.first().split(" ").map { it.toBigInteger() }
+}
+
+private fun BigInteger.getNrOfStonesAfter(blinks: Int, memoization: MutableMap<BigInteger, BigInteger>): Int {
+    if (blinks == 0) {
+        return 1
+    }
+
+    if (this == BigInteger.ZERO) {
+        val nrOfStones = BigInteger.ONE.getNrOfStonesAfter(blinks - 1, memoization)
+        //
+        return nrOfStones
+    } else {
+        val digit = this.toString()
+        if (digit.length % 2 == 0) {
+            val firstStone = digit.substring(0, digit.length / 2).toBigInteger()
+            val secondStone = digit.substring(digit.length / 2).toBigInteger()
+            return firstStone.getNrOfStonesAfter(blinks - 1, memoization) + secondStone.getNrOfStonesAfter(blinks - 1, memoization)
+        } else {
+            return (this * BigInteger.valueOf(2024)).getNrOfStonesAfter(blinks - 1, memoization)
+        }
+    }
+}
+
+private fun List<BigInteger>.blink(): List<BigInteger> {
+    return this.map {
+        val digit = it.toString()
+        if (it == BigInteger.ZERO) {
+            return@map listOf(BigInteger.ONE)
+        } else {
+            if (digit.length % 2 == 0) {
+                val firstStone = digit.substring(0, digit.length / 2).toBigInteger()
+                val secondStone = digit.substring(digit.length / 2).toBigInteger()
+                return@map listOf(firstStone, secondStone)
+            } else {
+                return@map listOf(it * BigInteger.valueOf(2024))
+            }
+        }
+    }.flatten()
+}

src/main/resources/aoc/year2024/Day11.txt

@@ -0,0 +1 @@
+572556 22 0 528 4679021 1 10725 2790