Solve day 12 part 1

aoc2024/src/main/kotlin/day12/Day12.kt

@@ -0,0 +1,60 @@
+package day12
+
+import common.*
+import java.io.File
+import java.io.InputStream
+import java.util.LinkedList
+import java.util.Queue
+import kotlin.streams.asSequence
+
+fun main() {
+    val input = parseInput(File("input/12.txt").inputStream())
+    println("Part 1: ${part1(input)}")
+}
+
+fun parseInput(stream: InputStream): Map<Vec, Char> {
+    return stream
+        .bufferedReader()
+        .lines()
+        .asSequence()
+        .flatMapIndexed { i, line -> line.mapIndexed { j, c -> Vec(i, j) to c }}
+        .toMap()
+}
+
+fun findRegionFor(pos: Vec, map: Map<Vec, Char>): Set<Vec> {
+    val regionChar = map[pos] ?: error("$pos not in map")
+    val region = mutableSetOf(pos)
+    val q: Queue<Vec> = LinkedList<Vec>().apply { add(pos) }
+    while (q.isNotEmpty()) {
+        val v = q.remove()
+        sequenceOf(Vec(1, 0), Vec(0, 1), Vec(-1, 0), Vec(0, -1))
+            .map { v + it }
+            .filter { !region.contains(it) && map.getOrDefault(it, '?') == regionChar }
+            .forEach { q.add(it); region.add(it) }
+    }
+    return region
+}
+
+fun getRegions(map: Map<Vec, Char>): List<Set<Vec>> {
+    val seen = mutableSetOf<Vec>()
+    val regions = mutableListOf<Set<Vec>>()
+    map.keys.forEach {
+        if (!seen.contains(it)) {
+            val region = findRegionFor(it, map)
+            regions.add(region)
+            seen.addAll(region)
+        }
+    }
+
+    return regions
+}
+
+fun part1(input: Map<Vec, Char>): Int {
+    return getRegions(input).sumOf { it.size * it.sumOf { pos -> perimeterScore(pos, input) }}
+}
+
+fun perimeterScore(pos: Vec, input: Map<Vec, Char>): Int {
+    val map = input.withDefault { '?' }
+    return sequenceOf(Vec(1, 0), Vec(0, 1), Vec(-1, 0), Vec(0, -1))
+        .count { map.getValue(pos) != map.getValue(pos + it) }
+}

aoc2024/src/test/kotlin/Day12Test.kt

@@ -0,0 +1,51 @@
+import common.Vec
+import day12.parseInput
+import day12.part1
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class Day12Test {
+    private val input1 = """
+        AAAA
+        BBCD
+        BBCC
+        EEEC
+    """.trimIndent()
+    private val input2 = """
+        OOOOO
+        OXOXO
+        OOOOO
+        OXOXO
+        OOOOO
+    """.trimIndent()
+    private val input3 = """
+        RRRRIICCFF
+        RRRRIICCCF
+        VVRRRCCFFF
+        VVRCCCJFFF
+        VVVVCJJCFE
+        VVIVCCJJEE
+        VVIIICJJEE
+        MIIIIIJJEE
+        MIIISIJEEE
+        MMMISSJEEE
+    """.trimIndent()
+
+    @Test
+    fun `Should parse input correctly`() {
+        val expected = mapOf(
+            Vec(0, 0) to 'A', Vec(0, 1) to 'A',Vec(0, 2) to 'A',Vec(0, 3) to 'A',
+            Vec(1, 0) to 'B', Vec(1, 1) to 'B',Vec(1, 2) to 'C',Vec(1, 3) to 'D',
+            Vec(2, 0) to 'B', Vec(2, 1) to 'B',Vec(2, 2) to 'C',Vec(2, 3) to 'C',
+            Vec(3, 0) to 'E', Vec(3, 1) to 'E',Vec(3, 2) to 'E',Vec(3, 3) to 'C',
+        )
+        assertEquals(expected, parseInput(input1.byteInputStream()))
+    }
+
+    @Test
+    fun testPart1() {
+//        assertEquals(140, part1(parseInput(input1.byteInputStream())))
+        assertEquals(772, part1(parseInput(input2.byteInputStream())))
+        assertEquals(1930, part1(parseInput(input3.byteInputStream())))
+    }
+}