2024 - Day 20 - part 1 & 2

src/main/kotlin/no/rodland/advent_2024/Day20.kt

@@ -1,26 +1,90 @@
 package no.rodland.advent_2024
 
-import no.rodland.advent.Day
+import no.rodland.advent.*
 
 // template generated: 20/12/2024
 // Fredrik Rødland 2024
 
-class Day20(val input: List<String>) : Day<Long, Long, List<String>> {
+class Day20(val input: List<String>, private val limit: Int = 0, private val limitTestPart2: Int = limit) : Day<Int, Int, Pair<Array<CharArray>, Pair<Pos, Pos>>> {
 
     private val parsed = input.parse()
+    private val racetrack: Cave = parsed.first
+    private val start = parsed.second.first
+    private val end = parsed.second.second
 
-    override fun partOne(): Long {
-        return 2
+    override fun partOne(): Int {
+        return solve(2, limit)
     }
 
-    override fun partTwo(): Long {
-        return 2
+    override fun partTwo(): Int {
+        return solve(20, limitTestPart2)
     }
 
-    override fun List<String>.parse(): List<String> {
-        return map { line ->
-            line
+    private fun solve(maxDistance: Int, lim: Int): Int {
+        val shortestPath = bfs(start, end)
+        val size = shortestPath.size
+        val fromStart = shortestPath.mapIndexed { idx, pos -> pos to idx }.toMap()
+        val toEnd = shortestPath.mapIndexed { idx, pos -> pos to size - idx }.toMap()
+        return shortestPath.asSequence().flatMapIndexed() { idx, from ->
+            shortestPath
+                .subList(idx + 1, shortestPath.size)
+                .mapNotNull { to ->
+                    val manhattanDistance = from.manhattanDistance(to)
+                    if (manhattanDistance in 2..maxDistance) {
+                        manhattanDistance to to
+                    } else {
+                        null
+                    }
+                }
+                .map { to ->
+                    size - (fromStart[from]!! + to.first + toEnd[to.second]!!)
+                }.filter { it > 0 }
         }
+            .groupBy { it }
+            .map { it.value.size to it.key }
+            .filter { it.second >= lim }
+            .sortedBy { it.second }
+            .sumOf { it.first }
+    }
+
+
+    private tailrec fun bfs(
+        start: Pos,
+        end: Pos,
+        queue: ArrayDeque<List<Pos>> = ArrayDeque(listOf(listOf(start))),
+        visited: MutableSet<Pos> = mutableSetOf(start)
+    ): List<Pos> {
+        if (queue.isEmpty()) return emptyList()
+        // Dequeue the current path
+        val path = queue.removeFirst()
+        val current = path.last()
+
+        // Check if we reached the end position
+        if (current == end) return path
+        current.neighbourCellsUDLR()
+            .filter { it !in visited }
+            .filter { it in racetrack }
+            .filter { racetrack[it] != '#' }
+            .forEach { neighbor ->
+                visited.add(neighbor)
+                queue.add(path + neighbor) // Enqueue the new path
+            }
+        // Recursive call with the updated queue and visited set
+        return bfs(start, end, queue, visited)
+    }
+
+    override fun List<String>.parse(): Pair<Array<CharArray>, Pair<Pos, Pos>> {
+        var start = Pos(0, 0)
+        var end = Pos(0, 0)
+        return this.mapIndexed { y, line ->
+            line.mapIndexed { x, c ->
+                when (c) {
+                    'S' -> start = Pos(x, y)
+                    'E' -> end = Pos(x, y)
+                }
+                c
+            }.toCharArray()
+        }.toTypedArray<CharArray>() to (start to end)
     }
 
     override val day = "20".toInt()

src/test/kotlin/no/rodland/advent_2024/Day20Test.kt

@@ -15,20 +15,22 @@ internal class Day20Test {
     private val data20 = "2024/input_20.txt".readFile()
     private val test20 = "2024/input_20_test.txt".readFile()
 
-    private val resultTestOne = 2L
-    private val resultTestTwo = 2L
-    private val resultOne = 2L
-    private val resultTwo = 2L
+    private val resultTestOne = 44
+    private val resultTestTwo = 285
+    private val resultOne = 1502
+    private val resultTwo = 1028136
 
     val test = defaultTestSuiteParseOnInit(
-        Day20(data20),
-        Day20(test20),
+        Day20(data20, 100),
+        Day20(test20, 0, 50),
         resultTestOne,
         resultOne,
         resultTestTwo,
         resultTwo,
-        { Day20(data20) },
+        { Day20(data20, 100) },
         { Day20(test20) },
+        numTestPart1 = 1,
+        numTestPart2 = 1,
     )
 
     @Nested

src/test/resources/2024/input_20_test.txt

@@ -0,0 +1,15 @@
+###############
+#...#...#.....#
+#.#.#.#.#.###.#
+#S#...#.#.#...#
+#######.#.#.###
+#######.#.#...#
+#######.#.###.#
+###..E#...#...#
+###.#######.###
+#...###...#...#
+#.#####.#.###.#
+#.#...#.#.#...#
+#.#.#.#.#.#.###
+#...#...#...###
+###############