Day 10: Hoof It

README.md

@@ -14,4 +14,4 @@ Development occurs in language-specific directories:
 |[Day7.hs](hs/src/Day7.hs)|[Day7.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day7.kt)|[day7.py](py/aoc2024/day7.py)|[day7.rs](rs/src/day7.rs)|
 |[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.hs](hs/src/Day10.hs)|[Day10.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day10.kt)|||

kt/aoc2024-exe/src/commonBench/kotlin/com/github/ephemient/aoc2024/exe/Day10Bench.kt

@@ -0,0 +1,31 @@
+package com.github.ephemient.aoc2024.exe
+
+import com.github.ephemient.aoc2024.Day10
+import kotlinx.benchmark.Benchmark
+import kotlinx.benchmark.Blackhole
+import kotlinx.benchmark.Scope
+import kotlinx.benchmark.Setup
+import kotlinx.benchmark.State
+
+@State(Scope.Benchmark)
+class Day10Bench {
+    private lateinit var input: String
+
+    @Setup
+    fun setup() {
+        input = getDayInput(10)
+    }
+
+    @Benchmark
+    fun part1() = Day10(input).part1()
+
+    @Benchmark
+    fun part2() = Day10(input).part2()
+
+    @Benchmark
+    fun solve(bh: Blackhole) {
+        val day10 = Day10(input)
+        bh.consume(day10.part1())
+        bh.consume(day10.part2())
+    }
+}

kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day10.kt

@@ -0,0 +1,41 @@
+package com.github.ephemient.aoc2024
+
+class Day10(input: String) {
+    private val levels: List<Set<IntPair>>
+    init {
+        val levels = List(10) { mutableSetOf<IntPair>() }
+        for ((y, line) in input.lineSequence().withIndex()) {
+            for ((x, char) in line.withIndex()) {
+                if (char.isDigit()) levels[char.digitToInt()].add(y to x)
+            }
+        }
+        this.levels = levels
+    }
+
+    private inline fun <T> bfs(start: (IntPair) -> T, plus: (T, T) -> T): Map<IntPair, T> =
+        levels.subList(1, 10).fold(levels[0].associateWith(start)) { acc, points ->
+            buildMap {
+                for ((key, value) in acc) {
+                    for (point in key.adj) {
+                        if (point in points) {
+                            put(point, if (contains(point)) plus(value, getValue(point)) else value)
+                        }
+                    }
+                }
+            }
+        }
+
+    fun part1() = bfs(::setOf, Set<IntPair>::plus).values.sumOf { it.size }
+
+    fun part2() = bfs({ 1 }, Int::plus).values.sum()
+
+    companion object {
+        private val IntPair.adj: List<IntPair>
+            get() = listOf(
+                first - 1 to second,
+                first to second - 1,
+                first to second + 1,
+                first + 1 to second,
+            )
+    }
+}

kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Days.kt

@@ -10,6 +10,7 @@ val days: List<Day> = listOf(
     Day(7, ::Day7, Day7::part1, Day7::part2),
     Day(8, ::Day8, Day8::part1, Day8::part2),
     Day(9, ::Day9, Day9::part1, Day9::part2),
+    Day(10, ::Day10, Day10::part1, Day10::part2),
 )
 
 data class Day(

kt/aoc2024-lib/src/commonTest/kotlin/com/github/ephemient/aoc2024/Day10Test.kt

@@ -0,0 +1,30 @@
+package com.github.ephemient.aoc2024
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class Day10Test {
+    @Test
+    fun part1() {
+        assertEquals(36, Day10(example).part1())
+    }
+
+    @Test
+    fun part2() {
+        assertEquals(81, Day10(example).part2())
+    }
+
+    companion object {
+        private val example =
+            """
+            |89010123
+            |78121874
+            |87430965
+            |96549874
+            |45678903
+            |32019012
+            |01329801
+            |10456732
+            |""".trimMargin()
+    }
+}