From 8b4384d5337e93741ca3a05aab95950533375333 Mon Sep 17 00:00:00 2001
From: Daniel Lin <ephemient@gmail.com>
Date: Wed, 11 Dec 2024 01:42:01 -0500
Subject: [PATCH] Day 11: Plutonian Pebbles

---
 README.md                                     |  2 +-
 .../ephemient/aoc2024/exe/Day11Bench.kt       | 31 ++++++++++++++
 .../com/github/ephemient/aoc2024/Day11.kt     | 42 +++++++++++++++++++
 .../com/github/ephemient/aoc2024/Days.kt      |  1 +
 .../com/github/ephemient/aoc2024/Day11Test.kt | 24 +++++++++++
 5 files changed, 99 insertions(+), 1 deletion(-)
 create mode 100644 kt/aoc2024-exe/src/commonBench/kotlin/com/github/ephemient/aoc2024/exe/Day11Bench.kt
 create mode 100644 kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day11.kt
 create mode 100644 kt/aoc2024-lib/src/commonTest/kotlin/com/github/ephemient/aoc2024/Day11Test.kt

diff --git a/README.md b/README.md
index 15f9a82..4ef7297 100644
--- a/README.md
+++ b/README.md
@@ -15,4 +15,4 @@ Development occurs in language-specific directories:
 |[Day8.hs](hs/src/Day8.hs)|[Day8.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day8.kt)|[day8.py](py/aoc2024/day8.py)|[day8.rs](rs/src/day8.rs)|
 |[Day9.hs](hs/src/Day9.hs)|[Day9.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day9.kt)|[day9.py](py/aoc2024/day9.py)|[day9.rs](rs/src/day9.rs)|
 |[Day10.hs](hs/src/Day10.hs)|[Day10.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day10.kt)|[day10.py](py/aoc2024/day10.py)|[day10.rs](rs/src/day10.rs)|
-|[Day11.hs](hs/src/Day11.hs)||||
+|[Day11.hs](hs/src/Day11.hs)|[Day11.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day11.kt)|||
diff --git a/kt/aoc2024-exe/src/commonBench/kotlin/com/github/ephemient/aoc2024/exe/Day11Bench.kt b/kt/aoc2024-exe/src/commonBench/kotlin/com/github/ephemient/aoc2024/exe/Day11Bench.kt
new file mode 100644
index 0000000..67c6bfa
--- /dev/null
+++ b/kt/aoc2024-exe/src/commonBench/kotlin/com/github/ephemient/aoc2024/exe/Day11Bench.kt
@@ -0,0 +1,31 @@
+package com.github.ephemient.aoc2024.exe
+
+import com.github.ephemient.aoc2024.Day11
+import kotlinx.benchmark.Benchmark
+import kotlinx.benchmark.Blackhole
+import kotlinx.benchmark.Scope
+import kotlinx.benchmark.Setup
+import kotlinx.benchmark.State
+
+@State(Scope.Benchmark)
+class Day11Bench {
+    private lateinit var input: String
+
+    @Setup
+    fun setup() {
+        input = getDayInput(11)
+    }
+
+    @Benchmark
+    fun part1() = Day11(input).part1()
+
+    @Benchmark
+    fun part2() = Day11(input).part2()
+
+    @Benchmark
+    fun solve(bh: Blackhole) {
+        val day11 = Day11(input)
+        bh.consume(day11.part1())
+        bh.consume(day11.part2())
+    }
+}
\ No newline at end of file
diff --git a/kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day11.kt b/kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day11.kt
new file mode 100644
index 0000000..57115e6
--- /dev/null
+++ b/kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day11.kt
@@ -0,0 +1,42 @@
+package com.github.ephemient.aoc2024
+
+class Day11(input: String) {
+    private val input = buildMap {
+        for (word in input.splitToSequence(WHITESPACE)) {
+            incBy(word.toLongOrNull() ?: continue, 1)
+        }
+    }
+
+    fun part1() = solve(25)
+
+    fun part2() = solve(75)
+
+    internal fun solve(n: Int): Long {
+        var counts = input
+        repeat(n) {
+            counts = buildMap {
+                for ((num, count) in counts) {
+                    if (num == 0L) {
+                        incBy(1, count)
+                    } else {
+                        val string = num.toString()
+                        if (string.length % 2 == 0) {
+                            incBy(string.take(string.length / 2).toLong(), count)
+                            incBy(string.drop(string.length / 2).toLong(), count)
+                        } else {
+                            incBy(2024 * num, count)
+                        }
+                    }
+                }
+            }
+        }
+        return counts.values.sum()
+    }
+
+    companion object {
+        private val WHITESPACE = """\s+""".toRegex()
+
+        private fun <K> MutableMap<K, Long>.incBy(key: K, value: Long) =
+            put(key, getOrElse(key) { 0 } + value)
+    }
+}
diff --git a/kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Days.kt b/kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Days.kt
index 7c172ee..7db5877 100644
--- a/kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Days.kt
+++ b/kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Days.kt
@@ -11,6 +11,7 @@ val days: List<Day> = listOf(
     Day(8, ::Day8, Day8::part1, Day8::part2),
     Day(9, ::Day9, Day9::part1, Day9::part2),
     Day(10, ::Day10, Day10::part1, Day10::part2),
+    Day(11, ::Day11, Day11::part1, Day11::part2),
 )
 
 data class Day(
diff --git a/kt/aoc2024-lib/src/commonTest/kotlin/com/github/ephemient/aoc2024/Day11Test.kt b/kt/aoc2024-lib/src/commonTest/kotlin/com/github/ephemient/aoc2024/Day11Test.kt
new file mode 100644
index 0000000..9ddf2e7
--- /dev/null
+++ b/kt/aoc2024-lib/src/commonTest/kotlin/com/github/ephemient/aoc2024/Day11Test.kt
@@ -0,0 +1,24 @@
+package com.github.ephemient.aoc2024
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class Day11Test {
+    @Test
+    fun part1() {
+        assertEquals(7, Day11(example1).solve(1))
+        assertEquals(22, Day11(example2).solve(6))
+        assertEquals(55312, Day11(example2).solve(25))
+    }
+
+    companion object {
+        private val example1 =
+            """
+            |0 1 10 99 999
+            |""".trimMargin()
+        private val example2 =
+            """
+            |125 17
+            |""".trimMargin()
+    }
+}