Day 08

input/day08

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+.............4....O..........w....R...............
+.................................f................
+..............4...j......NW0......................
+....................R..W..........................
+...............R..................................
+..................................................
+v.......................f.......0W................
+.....9L............l...N.........w................
+....L....9.......ON........8......................
+.1.........49L........f..0..N.....................
+..........................V...l...................
+..........4.......................................
+.....................j...................3.....U..
+....O.....U.......................................
+........J......................l..................
+.O....s.Q.......j.....l.....w..........F...q......
+..................................................
+.U.......................j..8.....................
+................U...............................3.
+2.............................J............3......
+..............................F...................
+.....s...R...........J..................F.........
+.s......................x..........F.....q........
+.......2.....Q........3........x..................
+...........v......................u...............
+..............v...........n......8............q...
+.......f..................8........i..............
+.5..................1n..............P.....i.......
+............7............Q..................X.....
+......5...p....................V..................
+.................J..........nx............q.......
+.......p............W...........................0.
+......2.............p.5.....1....P................
+......I.................7.X....i...P..............
+............s.....r...w................V..........
+...............or...6.................V...........
+............................PS.7..................
+..........o...........................S...........
+...........5..............o..1.......n............
+...........I.........r.......7.......6............
+.................o.r...........X..................
+................................x.........u.......
+.........p..Q....2................................
+.........v.................S.....................u
+I...........................S.....6...............
+..................................................
+.......I..........................................
+..................................................
+.......................................6..........
+.................................X................

src/day08.scala

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+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)