Day 08

src/day08.scala

@@ -0,0 +1,60 @@
+package aoc
+package day08
+
+val dayNumber = "08"
+
+@main def part1: Unit =
+  println(part1(loadInput(dayNumber)))
+
+@main def part2: Unit =
+  println(part2(loadInput(dayNumber)))
+
+def part1(input: String): String =
+  val (gridMap, antennas) = parseInput(input)
+  antennas.toList
+    .flatMap(positions =>
+      positions.combinations(2).flatMap { case List((ax, ay), (bx, by)) =>
+        val (diffX, diffY) = (bx - ax, by - ay)
+        List((ax - diffX, ay - diffY), (bx + diffX, by + diffY))
+      }
+    )
+    .distinct
+    .count(gridMap.get(_).isDefined)
+    .toString
+
+def part2(input: String): String =
+  val (gridMap, antennas) = parseInput(input)
+  antennas.toList
+    .flatMap(positions =>
+      positions.combinations(2).flatMap { case List((ax, ay), (bx, by)) =>
+        val (diffX, diffY) = (bx - ax, by - ay)
+        LazyList
+          .iterate(ax -> ay)((x, y) => (x - diffX, y - diffY))
+          .takeWhile(gridMap.get(_).isDefined) ++
+          LazyList
+            .iterate(bx -> by)((x, y) => (x + diffX, y + diffY))
+            .takeWhile(gridMap.get(_).isDefined) ++
+          List((ax, ay), (bx, by))
+      }
+    )
+    .distinct
+    .length
+    .toString
+
+def parseInput(
+    input: String
+): (Map[(Int, Int), Char], List[List[(Int, Int)]]) =
+  val grid = input.split("\n")
+  val coords =
+    for
+      y <- 0 until grid.length
+      x <- 0 until grid.head.length
+    yield (x, y) -> grid(y)(x)
+  val gridMap = coords.toMap
+  val antennas = coords
+    .filter(_._2 != '.')
+    .groupMap(_._2)(_._1)
+    .values
+    .map(_.toList)
+    .toList
+  (gridMap, antennas)