✨ day 18

src/main/scala/org/lemon/advent/year2024/Day18.scala

@@ -0,0 +1,27 @@
+package org.lemon.advent.year2024
+
+import org.lemon.advent.lib.`2d`._
+import org.lemon.advent.lib.graph._
+
+private object Day18:
+
+  def parse(input: String) = input.linesIterator.map(_ match
+    case s"$x,$y" => Coord(x.toInt, y.toInt)
+  ).toSeq
+
+  def adjacency(area: Area, corrupt: Set[Coord])(coord: Coord): Seq[Coord] =
+    coord.adjacent.filterNot(corrupt).filter(area.contains)
+
+  def part1(input: String, example: Boolean = false, take: Int = 1024) =
+    val area = if example then Area(0 to 6, 0 to 6) else Area(0 to 70, 0 to 70)
+    val corrupt = parse(input).take(take).toSet
+    pathFind(adjacency(area, corrupt), Coord(0, 0), area.bottomRight).get.distance
+
+  def part2(input: String, example: Boolean = false) =
+    val area = if example then Area(0 to 6, 0 to 6) else Area(0 to 70, 0 to 70)
+    val bytes = parse(input)
+    val lastPossible = bytes.reverse.tails.find(bits =>
+      pathFind(adjacency(area, bits.toSet), Coord(0, 0), area.bottomRight).isDefined
+    ).get
+    val impossible = bytes(lastPossible.size)
+    s"${impossible.x},${impossible.y}"

src/test/scala/org/lemon/advent/year2024/Day18Test.scala

@@ -0,0 +1,72 @@
+package org.lemon.advent.year2024
+
+import org.lemon.advent._
+import org.lemon.advent.year2024.Day18._
+
+class Day18Test extends UnitTest:
+
+  test("part 1 example") {
+    val in = """|5,4
+                |4,2
+                |4,5
+                |3,0
+                |2,1
+                |6,3
+                |2,4
+                |1,5
+                |0,6
+                |3,3
+                |2,6
+                |5,1
+                |1,2
+                |5,5
+                |2,5
+                |6,5
+                |1,4
+                |0,4
+                |6,4
+                |1,1
+                |6,1
+                |1,0
+                |0,5
+                |1,6
+                |2,0""".stripMargin
+    part1(in, example = true, take = 12) shouldBe 22
+  }
+
+  test("part 1") {
+    part1(read(file(2024)(18))) shouldBe 338
+  }
+
+  test("part 2 example") {
+    val in = """|5,4
+                |4,2
+                |4,5
+                |3,0
+                |2,1
+                |6,3
+                |2,4
+                |1,5
+                |0,6
+                |3,3
+                |2,6
+                |5,1
+                |1,2
+                |5,5
+                |2,5
+                |6,5
+                |1,4
+                |0,4
+                |6,4
+                |1,1
+                |6,1
+                |1,0
+                |0,5
+                |1,6
+                |2,0""".stripMargin
+    part2(in, example = true) shouldBe "6,1"
+  }
+
+  test("part 2") {
+    part2(read(file(2024)(18))) shouldBe "20,44"
+  }