✨ day 20 part 1; slowwww

src/main/scala/org/lemon/advent/year2024/Day20.scala

@@ -0,0 +1,45 @@
+package org.lemon.advent.year2024
+
+import org.lemon.advent.lib._
+import org.lemon.advent.lib.`2d`._
+import org.lemon.advent.lib.graph._
+
+private object Day20:
+
+  def parse = Coord.gridToMap
+
+  def findCheats(grid: Map[Coord, Char]): Seq[(Coord, Coord)] =
+    def isTrack(c: Char) = c == '.' || c == 'S' || c == 'E'
+    def get(coord: Coord) =
+      val c = grid.getOrElse(coord, ' ')
+      if isTrack(c) then '.' else c
+
+    grid.iterator
+      .filter((_, c) => isTrack(c))
+      .flatMap((coord, _) =>
+        for
+          d <- Direction.values
+          if get(coord.shift(d, 1)) == '#'
+          if get(coord.shift(d, 2)) == '.'
+        yield (coord, coord.shift(d, 2))
+      )
+      .toSeq.sorted
+
+  def adjacency(grid: Map[Coord, Char], cheat: (Coord, Coord))(coord: Coord) =
+    val neigh = coord.adjacent.filter(c => grid.getOrElse(c, '#') != '#').map((_, 1))
+    if coord == cheat._1 then (cheat._2, 2) +: neigh else neigh
+
+  def part1(input: String) =
+    val grid = parse(input)
+    val start = grid.find(_._2 == 'S').get._1
+    val end = grid.find(_._2 == 'E').get._1
+    val noCheating = pathFind(adjacency(grid, ((-1, -1), (-1, -1))), start, end).get.distance
+
+    val cheats = findCheats(grid)
+    cheats
+      .map(cheat => pathFind(adjacency(grid, cheat), start, end).get.distance)
+      .map(noCheating - _)
+      .count(_ >= 100)
+
+  def part2(input: String) =
+    0

src/test/scala/org/lemon/advent/year2024/Day20Test.scala

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+package org.lemon.advent.year2024
+
+import org.lemon.advent._
+import org.lemon.advent.year2024.Day20._
+
+class Day20Test extends UnitTest:
+
+  test("part 1 example") {
+    val in = """|###############
+                |#...#...#.....#
+                |#.#.#.#.#.###.#
+                |#S#...#.#.#...#
+                |#######.#.#.###
+                |#######.#.#...#
+                |#######.#.###.#
+                |###..E#...#...#
+                |###.#######.###
+                |#...###...#...#
+                |#.#####.#.###.#
+                |#.#...#.#.#...#
+                |#.#.#.#.#.#.###
+                |#...#...#...###
+                |###############""".stripMargin
+    part1(in) shouldBe 0
+  }
+
+  test("part 1") {
+    part1(read(file(2024)(20))) shouldBe 1289
+  }
+
+  test("part 2 example") {
+    val in = """|
+                |""".stripMargin
+    part2(in) shouldBe 0
+  }
+
+  test("part 2") {
+    part2(read(file(2024)(20))) shouldBe 0
+  }