day 10 puzzle 1

src/day10/Puzzle1.scala

@@ -0,0 +1,74 @@
+package day10
+
+import scala.collection.immutable.HashMap
+import scala.io.{BufferedSource, Source}
+
+object Puzzle1 {
+  var grid: Array[Array[Byte]] = Array.empty
+
+  // bits: NWSE
+  val TILES: Map[Char, Byte] = HashMap(
+    '|' -> 10,
+    '-' -> 5,
+    'L' -> 9,
+    'J' -> 12,
+    '7' -> 6,
+    'F' -> 3,
+    '.' -> 0,
+    'S' -> 15
+  )
+
+  var height: Int = 0
+  var width: Int = 0
+  var startX: Int = 0
+  var startY: Int = 0
+
+  def loadInput(path: String): Unit = {
+    val source: BufferedSource = Source.fromFile(path)
+    val lines: Array[String] = source.getLines().toArray
+
+    height = lines.length
+    width = if (height == 0) 0 else lines(0).length
+    grid = Array.ofDim(height, width)
+
+    for ((line: String, y: Int) <- lines.zipWithIndex) {
+      for ((c: Char, x: Int) <- line.zipWithIndex) {
+        grid(y)(x) = TILES(c)
+        if (c == 'S') {
+          startX = x
+          startY = y
+        }
+      }
+    }
+
+    source.close()
+  }
+
+  def calculateMaxDistance(): Int = {
+    val walker1: Walker = new Walker(startX, startY)
+    walker1.walk(grid)
+    val walker2: Walker = new Walker(startX, startY, walker1.getX(), walker1.getY())
+
+    while (walker1.getPos() != walker2.getPos()) {
+      walker2.walk(grid)
+      if (walker1.getPos() == walker2.getPos()) {
+        return walker2.getDistance()
+      }
+      walker1.walk(grid)
+    }
+    return walker1.getDistance()
+  }
+
+  def solve(path: String): Int = {
+    loadInput(path)
+
+    val solution: Int = calculateMaxDistance()
+
+    return solution
+  }
+
+  def main(args: Array[String]): Unit = {
+    val solution: Int = solve("./res/day10/input1.txt")
+    println(solution)
+  }
+}

src/day10/Walker.scala

@@ -0,0 +1,60 @@
+package day10
+
+class Walker {
+  private var x: Int = 0
+  private var y: Int = 0
+  private var lastX: Int = -1
+  private var lastY: Int = -1
+  private var distance: Int = 0
+
+  val OFFSETS: Array[(Int, Int)] = Array(
+    (1, 0), (0, 1), (-1, 0), (0, -1)
+  )
+
+  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) <- 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")
+  }
+}