Day 7 :(

src/aoc2025/Day07.kt

@@ -0,0 +1,84 @@
+package aoc2025
+
+import CharGrid
+import println
+import readInput
+
+/*
+--- Day 7: Laboratories ---
+https://adventofcode.com/2025/day/7
+*/
+fun main() {
+
+    val inlineTestInput = """
+.......S.......
+...............
+.......^.......
+...............
+......^.^......
+...............
+.....^.^.^.....
+...............
+....^.^...^....
+...............
+...^.^...^.^...
+...............
+..^...^.....^..
+...............
+.^.^.^.^.^...^.
+...............
+"""
+
+    val memo = ArrayList<HashMap<Int, Long>>()
+
+    fun part1(input: List<String>): Int {
+        val grid = CharGrid(input)
+        var splits = 0
+        for (row in 2 until grid.height step 2) {
+            for (col in 1 until grid.width - 1) {
+                val ch = grid[col, row - 2]
+                if (ch == 'S') {
+                    if (grid[col, row] == '^') {
+                        grid[col - 1, row] = 'S'
+                        grid[col + 1, row] = 'S'
+                        splits++
+                    } else {
+                        grid[col, row] = 'S'
+                    }
+                }
+            }
+        }
+        return splits
+    }
+
+    fun rec(grid: CharGrid, col: Int, row: Int): Long {
+        if (row >= grid.height) return 1
+        return memo[row / 2].getOrPut(col) {
+            if (grid[col, row + 2] == '^')
+                rec(grid, col - 1, row + 2) + rec(grid, col + 1, row + 2)
+            else
+                rec(grid, col, row + 2)
+        }
+    }
+
+    fun part2(input: List<String>): Long {
+        val grid = CharGrid(input)
+        val col = grid.collectMatches { it == 'S' }.single().second.dc
+        while (memo.size <= grid.height / 2) memo.add(HashMap())
+        return rec(grid, col, 0)
+    }
+
+    // test if implementation meets criteria from the description, like:
+    val testInput = inlineTestInput.trim().reader().readLines()
+    //val testInput = readInput("aoc2025/Day07_test")
+    val testInputPart1Result = part1(testInput)
+    println("Part 1 Test: $testInputPart1Result")
+    val testInputPart2Result = part2(testInput)
+    println("Part 2 Test: $testInputPart2Result")
+    check(testInputPart1Result == 21)
+    check(testInputPart2Result == 40L)
+
+    val input = readInput("aoc2025/Day07")
+    part1(input).println()
+    part2(input).println()
+}