Day 12 Part 2 not correct.

src/Utils.kt

@@ -196,6 +196,9 @@ class CharGrid {
     fun matchRelative(c: Int, r: Int, relposes: Iterable<RelPos>, predicate: (char: Char) -> Boolean): List<RelPos> =
         relposes.filter { predicate(get(c + it.dc, r + it.dr)) }
 
+    fun matchAbsoluteRelPos(pos: RelPos, relposes: Iterable<RelPos>, predicate: (char: Char) -> Boolean): List<RelPos> =
+        relposes.map { pos.translate(it) }.filter { predicate(get(it)) }
+
     fun marchMatching(pos: RelPos, relposes: Iterable<RelPos>, predicate: (char: Char) -> Boolean): List<RelPos> =
         relposes.map { pos.translate(it) }.filter { predicate(get(it)) }
 
@@ -215,7 +218,7 @@ class CharGrid {
         val topBottom = CharArray(width + 2) { borderChar }
         return CharGrid(Array(height + 2) {
             if (it == 0 || it == height + 1) topBottom else
-                CharArray(width + 2) { r -> if (r == 0 || r == width + 1) borderChar else get(it - 1, r - 1) }
+                CharArray(width + 2) { r -> if (r == 0 || r == width + 1) borderChar else get(r - 1, it - 1) }
         }, borderChar)
     }
 

src/aoc2024/Day12.kt

@@ -0,0 +1,122 @@
+package aoc2024
+
+import CharGrid
+import RelPos
+import println
+import readInput
+
+/*
+--- Day 12: Garden Groups ---
+https://adventofcode.com/2024/day/12
+*/
+fun main() {
+
+    val inlineTestInput = """
+RRRRIICCFF
+RRRRIICCCF
+VVRRRCCFFF
+VVRCCCJFFF
+VVVVCJJCFE
+VVIVCCJJEE
+VVIIICJJEE
+MIIIIIJJEE
+MIIISIJEEE
+MMMISSJEEE
+    """
+
+    fun part1(input: List<String>): Int {
+        val grid = CharGrid(input)
+        var sum = 0
+        for (p in grid.generateGridPos()) {
+            val c = grid[p]
+            if (c != '.') {
+                val areaPos = HashSet<RelPos>()
+                val fence = HashSet<RelPos>()
+                var newPos = setOf(p)
+                while (newPos.isNotEmpty()) {
+                    val newSeeds = HashSet<RelPos>()
+                    for (np in newPos) {
+                        areaPos.add(np)
+                        grid[np] = c.lowercaseChar()
+                        newSeeds.addAll(grid.matchAbsoluteRelPos(np, CharGrid.PLUS_POS) { it == c })
+                        fence.addAll(grid.matchRelative(np.dc, np.dr, CharGrid.PLUS_POS) { it.uppercaseChar() != c }
+                            .map { RelPos(np.dc * 2 + it.dc, np.dr * 2 + it.dr) })
+                    }
+                    newPos = newSeeds
+                }
+                areaPos.forEach { grid[it] = '.' }
+                sum += areaPos.size * fence.size
+            }
+        }
+        return sum
+    }
+
+    fun part2(input: List<String>): Int {
+        val grid = CharGrid(input)
+        var sum = 0
+        for (p in grid.generateGridPos()) {
+            val c = grid[p]
+            if (c != '.') {
+                println("$p: $c")
+                val areaPos = HashSet<RelPos>()
+                val fence = HashSet<RelPos>()
+                var newPos = setOf(p)
+                while (newPos.isNotEmpty()) {
+                    val newSeeds = HashSet<RelPos>()
+                    for (np in newPos) {
+                        areaPos.add(np)
+                        grid[np] = c.lowercaseChar()
+                        newSeeds.addAll(grid.matchAbsoluteRelPos(np, CharGrid.PLUS_POS) { it == c })
+                        fence.addAll(grid.matchRelative(np.dc, np.dr, CharGrid.BOX_POS) { it.uppercaseChar() != c }
+                            .map { RelPos(np.dc * 2 + it.dc, np.dr * 2 + it.dr) })
+                    }
+                    newPos = newSeeds
+                }
+                var turns = 0
+                while (fence.isNotEmpty()) {
+                    val f1 = fence.first()
+                    var dir = CharGrid.PLUS_POS.find { fence.contains(f1.translate(it)) }
+                    if (dir == null) {
+                        fence.remove(f1)
+                        turns += 2
+                        break
+                    }
+
+                    // 851006 too low
+                    // 852491 too high
+                    val initDir = dir
+                    var rp = f1
+                    while (fence.isNotEmpty()) {
+                        fence.remove(rp)
+                        if (fence.contains(rp.translate(dir!!))) {
+                            rp = rp.translate(dir)
+                        } else {
+                            dir = CharGrid.PLUS_POS.find { fence.contains(rp.translate(it)) } ?: break
+                            rp = rp.translate(dir)
+                            turns++
+                        }
+                    }
+                    if (initDir != dir) turns++
+                }
+                println("$c Area: ${areaPos.size} Fence: ${fence.size} Discount: $turns = ${areaPos.size * turns}")
+                areaPos.forEach { grid[it] = '.' }
+                sum += areaPos.size * turns
+            }
+        }
+        return sum
+    }
+
+    // test if implementation meets criteria from the description, like:
+    val testInput = inlineTestInput.trim().reader().readLines()
+    //val testInput = readInput("aoc2024/Day12_test")
+    val testInputPart1Result = part1(testInput)
+    println("Part 1 Test: $testInputPart1Result")
+    val testInputPart2Result = part2(testInput)
+    println("Part 2 Test: $testInputPart2Result")
+    check(testInputPart1Result == 1930)
+    check(testInputPart2Result == 1206)
+
+    val input = readInput("aoc2024/Day12")
+    part1(input).println()
+    part2(input).println()
+}