Day 10 part 1

2024/src/main/kotlin/day10.kt

@@ -0,0 +1,35 @@
+fun main() {
+    val map = CharGrid.read("day10.txt").map { it.digitToInt() }
+
+    val part1 = map.findCoordinatesOf(0)
+        .fold(0) { acc, start ->
+            acc + map.pathsToTop(start).size
+        }
+
+    println("Part 1: $part1")
+}
+
+fun <T> Grid<T>.findCoordinatesOf(value: T) = sequence {
+    for (y in 0..<height) {
+        for (x in 0..<width) {
+            if (get(x, y) == value) {
+                yield(Grid.Coordinate(x, y))
+            }
+        }
+    }
+}
+
+fun Grid<Int>.pathsToTop(coordinate: Grid.Coordinate): Set<Grid.Coordinate> {
+    val height = get(coordinate)
+
+    if (height == 9) {
+        return setOf(coordinate)
+    }
+
+    return Direction.entries
+        .map { coordinate.step(it) }
+        .filter { it in this && this[it] == height + 1 }
+        .fold(emptySet()) { acc, next ->
+            acc + pathsToTop(next)
+        }
+}