Day 10

aoc/src/dev/ctsk/aoc/Main.scala

@@ -11,7 +11,8 @@ val solvers = Map[Int, Solver](
   6 -> Day06,
   7 -> Day07,
   8 -> Day08,
-  9 -> Day09
+  9 -> Day09,
+  10 -> Day10
 )
 
 def runSolver(solver: Solver, input: os.Path): Unit =

aoc/src/dev/ctsk/aoc/days/Day10.scala

@@ -0,0 +1,46 @@
+package dev.ctsk.aoc.days
+
+import dev.ctsk.aoc._
+import dev.ctsk.aoc.Direction._
+
+object Day10 extends Solver(10):
+  type Input = (Grid[Char], Seq[Point])
+
+  def pre(input: os.ReadablePath): Input =
+    val grid = Grid(os.read.lines(input).map(_.toArray).toArray)
+    val zero = grid.find(_ == '0').toSeq
+    (grid, zero)
+
+  def step(
+      grid: Grid[Char],
+      start: Seq[(Point, Point)],
+      height: Int
+  ): Seq[(Point, Point)] =
+    (for
+      (p, origin) <- start
+      a <- Seq(Up, Down, Left, Right)
+      if grid(a(p)).exists(_.asDigit == height)
+    yield (a(p), origin))
+
+  def part1(input: Input): Int =
+    val (grid, zero) = input
+    (1 to 9)
+      .foldLeft(zero.zip(zero)) { case (acc, h) => step(grid, acc, h) }
+      .distinct
+      .size
+
+  def part2(input: Input): Int =
+    val (grid, zero) = input
+    (1 to 9)
+      .foldLeft(zero.zip(zero)) { case (acc, h) => step(grid, acc, h) }
+      .size
+
+  def run(input: os.ReadablePath): (Timings, Solution) =
+    val (pre_time, (grid, zero)) = timed { pre(input) }
+    val (p1_time, p1_solution) = timed { part1((grid, zero)) }
+    val (p2_time, p2_solution) = timed { part2((grid, zero)) }
+
+    (
+      Timings(pre_time, p1_time, p2_time),
+      Solution(Int.box(p1_solution), Int.box(p2_solution))
+    )