Add solution for Y2024D10.

Author: Jadarma

README.md

@@ -15,7 +15,7 @@ _"Anything that's worth doing, is worth overdoing."_
 Table of contents to jump straight to the problem you're looking for.
 
 <details open>
-    <summary>2024 (18x⭐)</summary>
+    <summary>2024 (20x⭐)</summary>
 
 | Day | Title                                                      | Stars |
 |:---:|:-----------------------------------------------------------|:-----:|
@@ -28,6 +28,7 @@ Table of contents to jump straight to the problem you're looking for.
 | 07  | [Bridge Repair](solutions/aockt/y2024/Y2024D07.kt)         |  ⭐⭐   |
 | 08  | [Resonant Collinearity](solutions/aockt/y2024/Y2024D08.kt) |  ⭐⭐   |
 | 09  | [Disk Fragmenter](solutions/aockt/y2024/Y2024D09.kt)       |  ⭐⭐   |
+| 10  | [Hoof It](solutions/aockt/y2024/Y2024D10.kt)               |  ⭐⭐   |
 
 </details>
 

inputs/aockt/y2024/d10/input.txt

@@ -0,0 +1,65 @@
+package aockt.y2024
+
+import aockt.util.parse
+import aockt.util.spacial.*
+import io.github.jadarma.aockt.core.Solution
+
+object Y2024D10 : Solution {
+
+    /** A hiking trail topographical map. */
+    private class TopographicMap(private val data: Grid<Int>) : Grid<Int> by data {
+
+        /** The locations of trailheads, or points with zero altitude. */
+        val trailHeads: Set<Point> = data.points().mapNotNull { (p, v) -> p.takeIf { v == 0 } }.toSet()
+
+        /**
+         * Calculates the score of this [trailHead], or how many peaks can be reached from here.
+         * If the point is not a trailhead, the score is 0.
+         */
+        fun scoreOf(trailHead: Point): Int = trailPathsFrom(trailHead, distinct = true).size
+
+        /**
+         * Calculates the rating of this [trailHead], or how many different routes you can take to reach a peak.
+         * If the point is not a trailhead, the rating is 0.
+         */
+        fun ratingOf(trailHead: Point): Int = trailPathsFrom(trailHead, distinct = false).size
+
+        /**
+         * Finds all the trail paths from the [start] point, and returns the location of their peaks.
+         * If the point is not a trailhead, returns an empty list.
+         * If [distinct], duplicate paths to the same peak are discarded.
+         */
+        private fun trailPathsFrom(start: Point, distinct: Boolean): List<Point> = buildList {
+            if (start !in trailHeads) return@buildList
+            val area = Area(width, height)
+            val visited = mutableSetOf<Point>()
+
+            fun recurse(point: Point) {
+                val altitude = data[point]
+
+                if (altitude == 9) {
+                    if (!distinct || point !in visited) add(point)
+                    visited.add(point)
+                }
+
+                Direction.all
+                    .asSequence()
+                    .map(point::move)
+                    .filter { it in area }
+                    .filter { data[it] == altitude + 1 }
+                    .forEach(::recurse)
+            }
+
+            recurse(start)
+        }
+    }
+
+    /** Parse the [input] and return the [TopographicMap] of the hiking region. */
+    private fun parseInput(input: String): TopographicMap = parse {
+        val data = Grid(input) { it.digitToInt() }
+        TopographicMap(data)
+    }
+
+    override fun partOne(input: String): Int = parseInput(input).run { trailHeads.sumOf(::scoreOf) }
+    override fun partTwo(input: String): Int = parseInput(input).run { trailHeads.sumOf(::ratingOf) }
+}

inputs/aockt/y2024/d10/solution_part1.txt

@@ -0,0 +1,36 @@
+package aockt.y2024
+
+import io.github.jadarma.aockt.test.AdventDay
+import io.github.jadarma.aockt.test.AdventSpec
+
+@AdventDay(2024, 10, "Hoof It")
+class Y2024D10Test : AdventSpec<Y2024D10>({
+
+    val example1 = """
+        0123
+        1234
+        8765
+        9876
+    """.trimIndent()
+
+    val example2 = """
+        89010123
+        78121874
+        87430965
+        96549874
+        45678903
+        32019012
+        01329801
+        10456732
+    """.trimIndent()
+
+    partOne {
+        example1 shouldOutput 1
+        example2 shouldOutput 36
+    }
+
+    partTwo {
+        example1 shouldOutput 16
+        example2 shouldOutput 81
+    }
+})