feat(2024/08): 2024 day 08

2024/day08.scala

@@ -0,0 +1,40 @@
+package `2024`.day08
+
+import prelude.*
+
+extension (a: Pos)
+  infix def deltas(b: Pos): Iterator[Pos] =
+    val delta = (b - a)
+    Iterator.iterate(a + delta)(_ + delta)
+
+case class Context(size: Size, antennaes: Map[Char, Vector[Pos]]):
+  def solve(fn: ((Pos, Pos)) => IterableOnce[Pos]) =
+    antennaes.values.flatMap(_.combinationsN(2).flatMap(fn)).toSet
+
+  lazy val part1 =
+    solve((a, b) => Vector(a + (a - b), b + (b - a))).filter(size.contains).size
+  lazy val part2 = solve((a, b) =>
+    (a deltas b).takeWhile(size.contains)
+      ++ (b deltas a).takeWhile(size.contains),
+  ).size
+
+object Context:
+  def apply(input: String): Context =
+    apply(input.linesIterator.map(_.toCharArray).toArray)
+
+  def apply(grid: Array[Array[Char]]): Context =
+    val size = Size(grid)
+    val antennaes = (for
+      y <- 0 until size.height
+      x <- 0 until size.width
+      c = grid(y)(x)
+      if c != '.' && c != '#'
+    yield c -> Pos(x, y)).toVector.groupMap(_._1)(_._2)
+    Context(size, antennaes)
+
+@main def main() =
+  val input = readInput(this).mkString
+  val ctx = Context(input)
+
+  println(ctx.part1)
+  println(ctx.part2)

2024/day08.test.scala

@@ -0,0 +1,65 @@
+package `2024`.day08
+
+import munit.FunSuite
+import prelude.|>
+
+val example =
+  """|......#....#
+     |...#....0...
+     |....#0....#.
+     |..#....0....
+     |....0....#..
+     |.#....A.....
+     |...#........
+     |#......#....
+     |........A...
+     |.........A..
+     |..........#.
+     |..........#.""".stripMargin |> Context.apply
+
+class Part1Test extends FunSuite:
+  test("two"):
+    """|..........
+       |...#......
+       |..........
+       |....a.....
+       |..........
+       |.....a....
+       |..........
+       |......#...
+       |..........
+       |..........""".stripMargin
+      |> Context.apply |> (ctx => assertEquals(ctx.part1, 2))
+
+  test("three"):
+    """|..........
+       |...#......
+       |#.........
+       |....a.....
+       |........a.
+       |.....a....
+       |..#.......
+       |......#...
+       |..........
+       |..........""".stripMargin
+      |> Context.apply |> (ctx => assertEquals(ctx.part1, 4))
+
+  test("example"):
+    assertEquals(example.part1, 14)
+
+class Part2Test extends FunSuite:
+  test("T T T"):
+    """|T....#....
+       |...T......
+       |.T....#...
+       |.........#
+       |..#.......
+       |..........
+       |...#......
+       |..........
+       |....#.....
+       |..........""".stripMargin
+      |> Context.apply |> (ctx => assertEquals(ctx.part2, 9))
+
+  test("example"):
+    assertEquals(example.part2, 34)

prelude/math.scala

@@ -8,6 +8,8 @@ extension (n: Int)
 
 final case class Pos(x: Int, y: Int):
   def +(p: Pos) = Pos(x + p.x, y + p.y)
+  def -(p: Pos) = Pos(x - p.x, y - p.y)
+  def *(n: Int) = Pos(x * n, y * n)
 
 final case class Size(width: Int, height: Int):
   inline def contains(p: Pos) =