Day 8: Resonant Collinearity

README.md

@@ -12,4 +12,4 @@ Development occurs in language-specific directories:
 |[Day5.hs](hs/src/Day5.hs)|[Day5.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day5.kt)|[day5.py](py/aoc2024/day5.py)|[day5.rs](rs/src/day5.rs)|
 |[Day6.hs](hs/src/Day6.hs)|[Day6.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day6.kt)|[day6.py](py/aoc2024/day6.py)|[day6.rs](rs/src/day6.rs)|
 |[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.hs](hs/src/Day8.hs)|[Day8.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day8.kt)|||

kt/aoc2024-exe/src/commonBench/kotlin/com/github/ephemient/aoc2024/exe/Day8Bench.kt

@@ -0,0 +1,31 @@
+package com.github.ephemient.aoc2024.exe
+
+import com.github.ephemient.aoc2024.Day8
+import kotlinx.benchmark.Benchmark
+import kotlinx.benchmark.Blackhole
+import kotlinx.benchmark.Scope
+import kotlinx.benchmark.Setup
+import kotlinx.benchmark.State
+
+@State(Scope.Benchmark)
+class Day8Bench {
+    private lateinit var input: String
+
+    @Setup
+    fun setup() {
+        input = getDayInput(8)
+    }
+
+    @Benchmark
+    fun part1() = Day8(input).part1()
+
+    @Benchmark
+    fun part2() = Day8(input).part2()
+
+    @Benchmark
+    fun solve(bh: Blackhole) {
+        val day8 = Day8(input)
+        bh.consume(day8.part1())
+        bh.consume(day8.part2())
+    }
+}

kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day8.kt

@@ -0,0 +1,47 @@
+package com.github.ephemient.aoc2024
+
+class Day8(input: String) {
+    private val height: Int
+    private val width: Int
+    private val antennae: Map<Char, List<IntPair>>
+    init {
+        val lines = input.trimEnd().lines()
+        height = lines.size
+        width = lines.maxOfOrNull { it.length } ?: 0
+        antennae = buildMap<Char, MutableList<IntPair>> {
+            for ((y, line) in lines.withIndex()) {
+                for ((x, char) in line.withIndex()) {
+                    if (char != '.') getOrPut(char) { mutableListOf() }.add(y to x)
+                }
+            }
+        }
+    }
+
+    private fun MutableCollection<IntPair>.addIfInRange(y: Int, x: Int): Boolean =
+        if (y in 0..<height && x in 0..<width) {
+            add(y to x)
+            true
+        } else false
+
+    private fun solve(allMultiples: Boolean): Int = buildSet {
+        for ((char, points) in antennae) {
+            for (p0 in points) {
+                for (p1 in points) {
+                    if (p0 == p1) continue
+                    val dy = p1.first - p0.first
+                    val dx = p1.second - p0.second
+                    if (!allMultiples) {
+                        addIfInRange(p1.first + dy, p1.second + dx)
+                    } else {
+                        var i = 0
+                        while (addIfInRange(p1.first + i * dy, p1.second + i * dx)) i++
+                    }
+                }
+            }
+        }
+    }.size
+
+    fun part1() = solve(false)
+
+    fun part2() = solve(true)
+}

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

@@ -8,6 +8,7 @@ val days: List<Day> = listOf(
     Day(5, ::Day5, Day5::part1, Day5::part2),
     Day(6, ::Day6, Day6::part1, Day6::part2),
     Day(7, ::Day7, Day7::part1, Day7::part2),
+    Day(8, ::Day8, Day8::part1, Day8::part2),
 )
 
 data class Day(

kt/aoc2024-lib/src/commonTest/kotlin/com/github/ephemient/aoc2024/Day8Test.kt

@@ -0,0 +1,34 @@
+package com.github.ephemient.aoc2024
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class Day8Test {
+    @Test
+    fun part1() {
+        assertEquals(14, Day8(example).part1())
+    }
+
+    @Test
+    fun part2() {
+        assertEquals(34, Day8(example).part2())
+    }
+
+    companion object {
+        private val example =
+            """
+            |............
+            |........0...
+            |.....0......
+            |.......0....
+            |....0.......
+            |......A.....
+            |............
+            |............
+            |........A...
+            |.........A..
+            |............
+            |............
+            |""".trimMargin()
+    }
+}