Day 3: Gear Ratios

kt/aoc2023-exe/src/commonTest/kotlin/com/github/ephemient/aoc2023/exe/Day3Bench.kt

@@ -0,0 +1,23 @@
+package com.github.ephemient.aoc2023.exe
+
+import com.github.ephemient.aoc2023.Day3
+import kotlinx.benchmark.Benchmark
+import kotlinx.benchmark.Scope
+import kotlinx.benchmark.Setup
+import kotlinx.benchmark.State
+
+@State(Scope.Benchmark)
+class Day3Bench {
+    private lateinit var input: String
+
+    @Setup
+    fun setup() {
+        input = getDayInput(3)
+    }
+
+    @Benchmark
+    fun part1() = Day3(input).part1()
+
+    @Benchmark
+    fun part2() = Day3(input).part2()
+}

kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day3.kt

@@ -0,0 +1,32 @@
+package com.github.ephemient.aoc2023
+
+class Day3(input: String) {
+    private val parts: Map<Pair<Int, Int>, List<Int>> = mutableMapOf<Pair<Int, Int>, MutableList<Int>>().apply {
+        val lines = input.trimEnd().lines()
+        for ((y, line) in lines.withIndex()) {
+            for (match in NUMBER.findAll(line)) {
+                val number = match.value.toInt()
+                for (y2 in (y - 1).coerceAtLeast(0)..(y + 1).coerceAtMost(lines.lastIndex)) {
+                    val line2 = lines[y2]
+                    val x0 = match.range.first - 1
+                    val x1 = match.range.last + 1
+                    for (x in x0.coerceAtLeast(0)..x1.coerceAtMost(line2.lastIndex)) {
+                        if (line2[x].isSymbol()) {
+                            getOrPut(x to y2) { mutableListOf() } += number
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    fun part1(): Int = parts.values.sumOf { it.sum() }
+
+    fun part2(): Int = parts.values.sumOf { if (it.size == 2) it[0] * it[1] else 0 }
+
+    companion object {
+        private val NUMBER = """\d+""".toRegex()
+
+        private fun Char.isSymbol(): Boolean = this != '.' && !isWhitespace() && !isDigit()
+    }
+}

kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Days.kt

@@ -3,6 +3,7 @@ package com.github.ephemient.aoc2023
 val days = listOf(
     Day(1, ::Day1, Day1::part1, Day1::part2),
     Day(2, ::Day2, Day2::part1, Day2::part2),
+    Day(3, ::Day3, Day3::part1, Day3::part2),
 )
 
 data class Day(

kt/aoc2023-lib/src/commonTest/kotlin/com/github/ephemient/aoc2023/Day3Test.kt

@@ -0,0 +1,32 @@
+package com.github.ephemient.aoc2023
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class Day3Test {
+    @Test
+    fun part1() {
+        assertEquals(4361, Day3(example).part1())
+    }
+
+    @Test
+    fun part2() {
+        assertEquals(467835, Day3(example).part2())
+    }
+
+    companion object {
+        private val example =
+            """
+            |467..114..
+            |...*......
+            |..35..633.
+            |......#...
+            |617*......
+            |.....+.58.
+            |..592.....
+            |......755.
+            |...$.*....
+            |.664.598..
+            |""".trimMargin()
+    }
+}