day 13

src/main/kotlin/de/linkel/aoc/Day13.kt

@@ -3,12 +3,92 @@ package de.linkel.aoc
 import de.linkel.aoc.base.AbstractLinesAdventDay
 import de.linkel.aoc.base.QuizPart
 import jakarta.inject.Singleton
+import kotlin.math.min
 
 @Singleton
 class Day13: AbstractLinesAdventDay<Int>() {
     override val day = 13
 
     override fun process(part: QuizPart, lines: Sequence<String>): Int {
-       return 0
+        return lines.split { it.isEmpty() }
+            .sumOf { rows ->
+                val cols = (0 until rows.first().length)
+                    .map { c ->
+                        rows.map { it[c] }.joinToString("")
+                    }
+                val mirroredRows = findReflection(rows)
+                val mirroredCols = findReflection(cols)
+
+                val aResult = mirroredCols + mirroredRows * 100
+                if (part == QuizPart.A) {
+                    aResult
+                } else {
+                    val mrows = rows.toMutableList()
+                    val mcols = cols.toMutableList()
+                    coordinates(rows.size, cols.size)
+                        .firstNotNullOf { pos ->
+                            val backup = mrows[pos.first][pos.second]
+                            val char = if (backup == '#') '.' else '#'
+                            mrows[pos.first] = mrows[pos.first].replaceIndex(pos.second, char)
+                            mcols[pos.second] = mcols[pos.second].replaceIndex(pos.first, char)
+
+                            val mirroredRows2 = findReflection(mrows, mirroredRows)
+                            val mirroredCols2 = findReflection(mcols, mirroredCols)
+                            val result = mirroredCols2 + mirroredRows2 * 100
+
+                            mrows[pos.first] = mrows[pos.first].replaceIndex(pos.second, backup)
+                            mcols[pos.second] = mcols[pos.second].replaceIndex(pos.first, backup)
+
+                            result.takeIf { it != 0 }
+                        }
+                }
+            }
+    }
+
+    private fun findReflection(input: List<String>, except: Int = -1): Int {
+        return (1 until input.size)
+            .filter { it != except }
+            .firstNotNullOfOrNull { divider ->
+                val size = min(divider, input.size - divider)
+                val top = input.subList(divider - size, divider)
+                val bottom = input.subList(divider, divider + size).reversed()
+                if (top == bottom)
+                    divider
+                else null
+            } ?: 0
+    }
+}
+
+fun String.replaceIndex(idx: Int, char: Char): String {
+    return "${this.substring(0, idx)}$char${this.substring(idx+1)}"
+}
+
+fun coordinates(rows: Int, cols: Int): Sequence<Pair<Int, Int>> {
+    return sequence {
+        (0 until rows)
+            .forEach { r ->
+                (0 until cols)
+                    .forEach { c ->
+                            yield(r to c)
+                    }
+            }
+    }
+}
+
+fun <T> Sequence<T>.split(predicate: (T) -> Boolean): Sequence<List<T>> {
+    val input = this
+    return sequence {
+        val buffer = mutableListOf<T>()
+        input.forEach { element ->
+            if (predicate(element)) {
+                yield(buffer.toList())
+                buffer.clear()
+            } else {
+                buffer.add(element)
+            }
+        }
+        if (buffer.isNotEmpty()) {
+            yield(buffer.toList())
+        }
     }
 }

src/test/kotlin/de/linkel/aoc/Day13Test.kt

@@ -2,12 +2,42 @@ package de.linkel.aoc
 
 class Day13Test: AbstractDayTest<Int>() {
     override val exampleA = """
+#.##..##.
+..#.##.#.
+##......#
+##......#
+..#.##.#.
+..##..##.
+#.#.##.#.
+
+#...##..#
+#....#..#
+..##..###
+#####.##.
+#####.##.
+..##..###
+#....#..#
         """.trimIndent()
-    override val exampleSolutionA = 0
-    override val solutionA = 0
+    override val exampleSolutionA = 405
+    override val solutionA = 29213
 
-    override val exampleSolutionB = 0
-    override val solutionB = 0
+    override val exampleSolutionB = 400
+    override val solutionB = 37453
 
     override val implementation = Day13()
 }
+
+/*
+         9
+0 2 4 6 8
+ 1 3 5 7
+
+#...##..#   0
+#....#..#   1
+..##..###   2
+#####.##.   3
+#####.##.   4
+..##..###   5
+#....#..#   6
+             7
+ */