2024 - Day 11 - part 1 & 2

src/main/kotlin/no/rodland/advent_2024/Day11.kt

@@ -5,23 +5,60 @@ import no.rodland.advent.Day
 // template generated: 11/12/2024
 // Fredrik Rødland 2024
 
-class Day11(val input: List<String>) : Day<Long, Long, List<String>> {
+class Day11(val input: List<String>) : Day<Long, Long, List<Long>> {
 
     private val parsed = input.parse()
-
     override fun partOne(): Long {
-        return 2
+        val memoization = mutableMapOf<Pair<Long, Int>, Long>()
+        return parsed.map { it.numberStones(25, memoization) }.sumOf { it }
     }
 
     override fun partTwo(): Long {
-        return 2
+        val memoization = mutableMapOf<Pair<Long, Int>, Long>()
+        return parsed.map { it.numberStones(75, memoization) }.sumOf { it }
+    }
+
+    private fun Long.numberStones(i: Int, memoization: MutableMap<Pair<Long, Int>, Long>): Long {
+        if (i == 0) return 1
+        if (memoization.containsKey(this to i)) {
+            return memoization[this to i]!!
+        }
+        return this.runRules().sumOf { it.numberStones(i - 1, memoization) }.also { memoization[this to i] = it }
+    }
+
+    private fun Long.runRules(): List<Long> {
+        return when {
+            this == 0L -> listOf(1L)
+            this.evenDigits() -> this.split()
+            else -> listOf(2024 * this)
+        }
+    }
+
+    private fun Long.split(): List<Long> = "$this".let {
+        val middle = "$this".length / 2
+        listOf(it.substring(0, middle).toLong(), it.substring(middle).toLong())
     }
 
-    override fun List<String>.parse(): List<String> {
-        return map { line ->
-            line
+    private fun Long.evenDigits(): Boolean = "$this".length % 2 == 0
+
+    @Suppress("unused")
+    fun partOneBruteForce(): Long {
+        var l = parsed
+        repeat(25) {
+            l = l.fold(emptyList()) { acc, num ->
+                acc + num.runRules()
+            }
         }
+        return l.size.toLong()
+    }
+
+    override fun List<String>.parse(): List<Long> {
+        return first().split("\\s+".toRegex()).map { it.toLong() }
     }
 
     override val day = "11".toInt()
 }
+
+
+
+

src/test/kotlin/no/rodland/advent_2024/Day11Test.kt

@@ -15,10 +15,10 @@ internal class Day11Test {
     private val data11 = "2024/input_11.txt".readFile()
     private val test11 = "2024/input_11_test.txt".readFile()
 
-    private val resultTestOne = 2L
-    private val resultTestTwo = 2L
-    private val resultOne = 2L
-    private val resultTwo = 2L
+    private val resultTestOne = 55312L
+    private val resultTestTwo = 65601038650482L
+    private val resultOne = 172484L
+    private val resultTwo = 205913561055242L
 
     val test = defaultTestSuiteParseOnInit(
         Day11(data11),
@@ -29,6 +29,8 @@ internal class Day11Test {
         resultTwo,
         { Day11(data11) },
         { Day11(test11) },
+        numTestPart1 = 100,
+        numTestPart2 = 3
     )
 
     @Nested

src/test/resources/2024/input_11_test.txt

@@ -0,0 +1 @@
+125 17