day 18 puzzle 1

src/day18/Painter.scala

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+package day18
+
+import scala.collection.mutable.ArrayBuffer
+
+class Painter(startX: Int, startY: Int, excludeX: Int, excludeY: Int) extends Walker(startX, startY, excludeX, excludeY) {
+  def walk(grid: Array[Array[Byte]], zones: Array[Array[Int]], path: ArrayBuffer[(Int, Int)]): Unit = {
+    val prevX: Int = lastX
+    val prevY: Int = lastY
+    val curX: Int = x
+    val curY: Int = y
+    val curTile: Byte = grid(y)(x)
+    super.walk(grid)
+    val newX: Int = x
+    val newY: Int = y
+    val dx: Int = newX - prevX
+    val dy: Int = newY - prevY
+
+    // West-East
+    if (curTile == 5) {
+      // Going east
+      if (dx > 0) {
+        setZone(path, zones, curX, curY - 1, 1)
+        setZone(path, zones, curX, curY + 1, 2)
+
+        // Going west
+      } else {
+        setZone(path, zones, curX, curY - 1, 2)
+        setZone(path, zones, curX, curY + 1, 1)
+      }
+
+    // North-South
+    } else if (curTile == 10) {
+      // Going south
+      if (dy > 0) {
+        setZone(path, zones, curX+1, curY, 1)
+        setZone(path, zones, curX-1, curY, 2)
+
+      // Going north
+      } else {
+        setZone(path, zones, curX+1, curY, 2)
+        setZone(path, zones, curX-1, curY, 1)
+      }
+
+    // Corner
+    } else if (curTile != 15) {
+      val east: Boolean = (curTile & 1) != 0
+      val south: Boolean = (curTile & 2) != 0
+
+      val toEast: Boolean = dx > 0
+      val toSouth: Boolean = dy > 0
+
+      val offsetBottom: Boolean = east ^ toEast ^ toSouth
+      val zoneY: Boolean = !toSouth ^ east
+
+      val offsetRight: Boolean = south ^ toEast ^ toSouth
+      val zoneX: Boolean = toEast ^ south
+
+      val offsetY: Int = if (offsetBottom) 1 else -1
+      val zoneYVal: Int = if (zoneY) 2 else 1
+      setZone(path, zones, curX, curY+offsetY, zoneYVal)
+
+      val offsetX: Int = if (offsetRight) 1 else -1
+      val zoneXVal: Int = if (zoneX) 2 else 1
+      setZone(path, zones, curX+offsetX, curY, zoneXVal)
+    }
+  }
+
+  private def setZone(path: ArrayBuffer[(Int, Int)], zones: Array[Array[Int]], posX: Int, posY: Int, zone: Int): Unit = {
+    val height: Int = zones.length
+    val width: Int = if (height == 0) 0 else zones(0).length
+    if (0 <= posX && posX < width && 0 <= posY && posY < height) {
+      if (!path.contains((posX, posY))) {
+        zones(posY)(posX) = zone
+      }
+    }
+  }
+}

src/day18/Puzzle1.scala

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+package day18
+
+import util.Ansi
+
+import scala.collection.immutable.HashMap
+import scala.collection.mutable.ArrayBuffer
+import scala.io.{BufferedSource, Source}
+
+object Puzzle1 {
+  var grid: Array[Array[Byte]] = Array.empty
+  var zones: Array[Array[Int]] = Array.empty
+
+  val OFFSETS: Array[(Int, Int)] = Array(
+    (1, 0), (0, 1), (-1, 0), (0, -1)
+  )
+  val DIRS: String = "RDLU"
+
+  // bits: NWSE
+  val TILES: Map[Char, Byte] = HashMap(
+    '|' -> 10,
+    '-' -> 5,
+    'L' -> 9,
+    'J' -> 12,
+    '7' -> 6,
+    'F' -> 3,
+    '.' -> 0,
+    'S' -> 15
+  )
+
+  val TILE_CHARS: Map[Int, Char] = HashMap(
+    10 -> '│',
+    5 -> '─',
+    9 -> '└',
+    12 -> '┘',
+    6 -> '┐',
+    3 -> '┌',
+    0 -> ' ',
+    15 -> '█'
+  )
+
+  val TILE_CHARS_BOLD: Map[Int, Char] = HashMap(
+    10 -> '┃',
+    5 -> '━',
+    9 -> '┗',
+    12 -> '┛',
+    6 -> '┓',
+    3 -> '┏',
+    0 -> ' ',
+    15 -> '█'
+  )
+
+  var height: Int = 0
+  var width: Int = 0
+  var startX: Int = 0
+  var startY: Int = 0
+  var path: ArrayBuffer[(Int, Int)] = new ArrayBuffer()
+
+  def loadInput(path: String): Unit = {
+    val source: BufferedSource = Source.fromFile(path)
+    val lines: Array[String] = source.getLines().toArray
+
+    var x: Int = 0
+    var y: Int = 0
+
+    var minX: Int = 0
+    var minY: Int = 0
+    var maxX: Int = 0
+    var maxY: Int = 0
+
+    for (line: String <- lines) {
+      val parts: Array[String] = line.split(" ")
+      val dir: Int = DIRS.indexOf(parts(0))
+      val dist: Int = parts(1).toInt
+      val offset: (Int, Int) = OFFSETS(dir)
+      x += offset._1*dist
+      y += offset._2*dist
+      minX = math.min(minX, x)
+      minY = math.min(minY, y)
+      maxX = math.max(maxX, x)
+      maxY = math.max(maxY, y)
+    }
+
+    width = maxX - minX + 1
+    height = maxY - minY + 1
+
+    grid = Array.ofDim(height, width)
+    zones = Array.ofDim(height, width)
+
+    x = -minX
+    y = -minY
+    var prevDir: Int = DIRS.indexOf(lines.last.split(" ")(0))
+    startX = x
+    startY = y
+
+    for ((line: String, i: Int) <- lines.zipWithIndex) {
+      val parts: Array[String] = line.split(" ")
+      val dir: Int = DIRS.indexOf(parts(0))
+      val dist: Int = parts(1).toInt
+      val offset: (Int, Int) = OFFSETS(dir)
+
+      for (_: Int <- 0 until dist) {
+        val prevBit: Int = 1 << ((prevDir + 2) % 4)
+        val curBit: Int = 1 << dir
+        grid(y)(x) = (prevBit| curBit).toByte
+        x += offset._1
+        y += offset._2
+        prevDir = dir
+      }
+    }
+
+    source.close()
+  }
+
+  def display(): Unit = {
+    for (y: Int <- 0 until height) {
+      for (x: Int <- 0 until width) {
+        val tile: Byte = grid(y)(x)
+        val zone: Int = zones(y)(x)
+        if (zone == 1) {
+          print(Ansi.BG_RGB(163, 61, 61))
+        } else if (zone == 2) {
+          print(Ansi.BG_RGB(77, 163, 61))
+        }
+        if (path.contains((x, y))) {
+          print(Ansi.BOLD)
+          print(TILE_CHARS_BOLD(tile))
+        } else {
+          print(TILE_CHARS(tile))
+        }
+        print(Ansi.CLEAR)
+      }
+      println()
+    }
+  }
+
+  def calculateArea(): Int = {
+    path = new ArrayBuffer()
+    path.addOne((startX, startY))
+
+    val walker: Walker = new Walker(startX, startY)
+
+    do {
+      walker.walk(grid)
+      path.addOne(walker.getPos())
+    } while (walker.getX() != startX || walker.getY() != startY)
+    println(s"Found path (length = ${path.length})")
+
+    val painter: Painter = new Painter(startX, startY, 2*startX-path(1)._1, 2*startY-path(1)._2)
+    do {
+      painter.walk(grid, zones, path)
+    } while (painter.getX() != startX || painter.getY() != startY)
+    println("Painted path neighbours")
+
+    var newZones: Array[Array[Int]] = Array.ofDim(height, width)
+    var changed: Boolean = true
+    var exteriorZone: Int = 0
+
+    do {
+      changed = false
+      newZones = copyZones()
+      for (y: Int <- 0 until height) {
+        for (x: Int <- 0 until width) {
+          if (zones(y)(x) != 0) {
+            if (floodTile(x, y, newZones, path)) {
+              changed = true
+            }
+          }
+        }
+      }
+      zones = newZones
+    } while (changed)
+    println("Flooded zones")
+
+    for (y: Int <- 0 until height) {
+      for (x: Int <- 0 until width) {
+        if (x == 0 || x == width - 1 || y == 0 || y == height - 1) {
+          if (zones(y)(x) != 0) {
+            exteriorZone = zones(y)(x)
+          }
+        }
+      }
+    }
+    println(s"Found exterior zone: $exteriorZone")
+
+    var area: Int = 0
+    for (y: Int <- 0 until height) {
+      for (x: Int <- 0 until width) {
+        if (zones(y)(x) != exteriorZone) area += 1
+      }
+    }
+    println(s"Calculated area: $area")
+
+    return area
+  }
+
+  def floodTile(x: Int, y: Int, newZones: Array[Array[Int]], path: ArrayBuffer[(Int, Int)]): Boolean = {
+    var changed: Boolean = false
+    for ((dx: Int, dy: Int) <- Walker.OFFSETS) {
+      val x2: Int = x + dx
+      val y2: Int = y + dy
+      if (0 <= x2 && x2 < width && 0 <= y2 && y2 < height) {
+        if (zones(y2)(x2) == 0 && !path.contains((x2, y2))) {
+          newZones(y2)(x2) = zones(y)(x)
+          changed = true
+        }
+      }
+    }
+    return changed
+  }
+
+  def copyZones(): Array[Array[Int]] = {
+    val result: Array[Array[Int]] = Array.ofDim(height, width)
+    for (y: Int <- 0 until height) {
+      for (x: Int <- 0 until width) {
+        result(y)(x) = zones(y)(x)
+      }
+    }
+    return result
+  }
+
+  def solve(path: String): Int = {
+    loadInput(path)
+
+    val solution: Int = calculateArea()
+
+    return solution
+  }
+
+  def main(args: Array[String]): Unit = {
+    val solution: Int = solve("./res/day18/input1.txt")
+    println(solution)
+    //display()
+  }
+}

src/day18/Walker.scala

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+package day18
+
+class Walker {
+  protected var x: Int = 0
+  protected var y: Int = 0
+  protected var lastX: Int = -1
+  protected var lastY: Int = -1
+  protected var distance: Int = 0
+
+  def this(startX: Int, startY: Int) = {
+    this()
+    x = startX
+    y = startY
+  }
+
+  def this(startX: Int, startY: Int, excludeX: Int, excludeY: Int) = {
+    this(startX, startY)
+    lastX = excludeX
+    lastY = excludeY
+  }
+
+  def getX(): Int = x
+  def getY(): Int = y
+  def getPos(): (Int, Int) = (x, y)
+  def getDistance(): Int = distance
+
+  def walk(grid: Array[Array[Byte]]): Unit = {
+    val height: Int = grid.length
+    val width: Int = if (height == 0) 0 else grid(0).length
+    val (x2: Int, y2: Int) = getNextPos(grid, width, height)
+    lastX = x
+    lastY = y
+    x = x2
+    y = y2
+    distance += 1
+  }
+
+  private def getNextPos(grid: Array[Array[Byte]], width: Int, height: Int): (Int, Int) = {
+    val curTile: Byte = grid(y)(x)
+    for (((dx: Int, dy: Int), i: Int) <- Walker.OFFSETS.zipWithIndex) {
+      val x2: Int = x + dx
+      val y2: Int = y + dy
+      if (x2 != lastX || y2 != lastY) {
+        if (0 <= x2 && x2 < width && 0 <= y2 && y2 < height) {
+          val bit: Byte = (1 << i).toByte
+          val bit2: Byte = (1 << ((i + 2) % 4)).toByte
+          if ((curTile & bit) != 0 && (grid(y2)(x2) & bit2) != 0) {
+            return (x2, y2)
+          }
+        }
+      }
+    }
+
+    throw new Exception("Dead-end path")
+  }
+}
+
+object Walker {
+  val OFFSETS: Array[(Int, Int)] = Array(
+    (1, 0), (0, 1), (-1, 0), (0, -1)
+  )
+}

tests/day18/Puzzle1Test.scala

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+package day18
+
+import org.scalatest.funsuite.AnyFunSuite
+
+class Puzzle1Test extends AnyFunSuite {
+  test("Puzzle1.solve") {
+    assert(Puzzle1.solve("tests_res/day18/input1.txt") == 62)
+  }
+}

tests_res/day18/input1.txt

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+R 6 (#70c710)
+D 5 (#0dc571)
+L 2 (#5713f0)
+D 2 (#d2c081)
+R 2 (#59c680)
+D 2 (#411b91)
+L 5 (#8ceee2)
+U 2 (#caa173)
+L 1 (#1b58a2)
+U 2 (#caa171)
+R 2 (#7807d2)
+U 3 (#a77fa3)
+L 2 (#015232)
+U 2 (#7a21e3)