day 8 puzzle 2 (naive and not optimized)

README.md

@@ -5,11 +5,11 @@ This repo contains my attempt at this year's Advent of Code (2023)
 I will try and do some problems (probably not all of them) in Scala
 
 ## Progress:
-#### Stars: 15 / 50
+#### Stars: 16 / 50
 |        Mon        |        Tue        |        Wed        |        Thu        |        Fri        |        Sat        |        Sun        |
 |:-----------------:|:-----------------:|:-----------------:|:-----------------:|:-----------------:|:-----------------:|:-----------------:|
 |                   |                   |                   |                   | 1<br>:star::star: | 2<br>:star::star: | 3<br>:star::star: |
-| 4<br>:star::star: | 5<br>:star::star: | 6<br>:star::star: | 7<br>:star::star: |    8<br>:star:    |         9         |        10         |
+| 4<br>:star::star: | 5<br>:star::star: | 6<br>:star::star: | 7<br>:star::star: | 8<br>:star::star: |         9         |        10         |
 |        11         |        12         |        13         |        14         |        15         |        16         |        17         |
 |        18         |        19         |        20         |        21         |        22         |        23         |        24         |
 |        25         |                   |                   |                   |                   |                   |                   |

src/day8/Ghost.scala

@@ -0,0 +1,80 @@
+package day8
+
+import scala.collection.mutable
+import scala.collection.mutable.ArrayBuffer
+
+class Ghost(val startId: String) extends Iterator[Long] {
+  var preLoopOffsets: ArrayBuffer[Int] = new ArrayBuffer()
+  var loopOffsets: ArrayBuffer[Int] = new ArrayBuffer()
+  var visited: ArrayBuffer[(String, Int)] = new ArrayBuffer()
+  private var distIterator: Iterator[Long] = Iterator.empty
+
+  def computePath(nodes: mutable.Map[String, Node], rule: Array[Int]): Unit = {
+    var id: String = startId
+    preLoopOffsets.addOne(0)
+    var ruleI: Int = 0
+
+    // While not looped
+    while (!visited.contains((id, ruleI))) {
+      //println(s"  Visited $id (ruleI = $ruleI)")
+      visited.addOne((id, ruleI))
+      id = nodes(id).nextNodes(rule(ruleI))
+      preLoopOffsets(preLoopOffsets.length-1) += 1
+      ruleI = (ruleI + 1) % rule.length
+      if (id.last == 'Z') {
+        preLoopOffsets.addOne(0)
+      }
+    }
+
+    val loopStartDist: Int = visited.indexOf((id, ruleI))
+    var dist: Int = 0
+    var loopStartI: Int = 0
+    while (dist < loopStartDist) {
+      dist += preLoopOffsets(loopStartI)
+      loopStartI += 1
+    }
+    loopStartI -= 1
+    preLoopOffsets(preLoopOffsets.length-1) += preLoopOffsets(loopStartI) - loopStartDist
+    println(s"  Loop from ($id, $ruleI) (index=$loopStartI)")
+    println(s"  # of offsets: ${preLoopOffsets.length}")
+
+    loopOffsets.addAll(preLoopOffsets.drop(loopStartI+1))
+    preLoopOffsets = preLoopOffsets.dropRight(preLoopOffsets.length - loopStartI - 1)
+    println(preLoopOffsets.length)
+    println(loopOffsets.length)
+    distIterator = new GhostIterator(preLoopOffsets.toArray, loopOffsets.toArray)
+  }
+
+  override def hasNext: Boolean = true
+
+  override def next(): Long = distIterator.next()
+
+  private class GhostIterator(val preLoopOffsets: Array[Int], val loopOffsets: Array[Int]) extends Iterator[Long] {
+    private var inLoop: Boolean = false
+    private var offsetI: Int = 0
+    private var dist: Long = 0
+    override def hasNext: Boolean = true
+
+    override def next(): Long = {
+      var offset: Int = 0
+      if (inLoop) {
+        offset = loopOffsets(offsetI)
+      } else {
+        offset = preLoopOffsets(offsetI)
+      }
+      dist += offset
+
+      offsetI += 1
+      if (!inLoop) {
+        if (offsetI == preLoopOffsets.length) {
+          offsetI = 0
+          inLoop = true
+        }
+      } else {
+        offsetI %= loopOffsets.length
+      }
+
+      return dist
+    }
+  }
+}

src/day8/Puzzle2.scala

@@ -0,0 +1,56 @@
+package day8
+
+import scala.collection.mutable
+import scala.io.{BufferedSource, Source}
+import scala.util.matching.Regex
+import scala.util.matching.Regex.Match
+
+object Puzzle2 {
+  var rule: Array[Int] = Array.empty
+  val nodes: mutable.Map[String, Node] = new mutable.HashMap()
+  var ghosts: Array[Ghost] = Array.empty
+  def loadInput(path: String): Unit = {
+    val source: BufferedSource = Source.fromFile(path)
+    val lines: String = source.getLines().mkString("\n")
+    val parts: Array[String] = lines.split("\n\n")
+
+    rule = parts(0).map(c => "LR".indexOf(c)).toArray
+    val regexp: Regex = new Regex("([A-Z]{3}) = \\(([A-Z]{3}), ([A-Z]{3})\\)")
+    for (line: String <- parts(1).split("\n")) {
+      val matches: Match = regexp.findFirstMatchIn(line).get
+      val id: String = matches.group(1)
+      val left: String = matches.group(2)
+      val right: String = matches.group(3)
+      nodes(id) = new Node(id, Array(left, right))
+    }
+
+    source.close()
+  }
+
+  def solve(path: String): Long = {
+    loadInput(path)
+
+    ghosts = nodes.keys.filter(k => k.last == 'A').map(k => new Ghost(k)).toArray
+
+    val ghostDists: mutable.Map[Ghost, Long] = new mutable.HashMap()
+    for (ghost: Ghost <- ghosts) {
+      println(s"Ghost from ${ghost.startId}")
+      ghost.computePath(nodes, rule)
+      ghostDists(ghost) = ghost.next()
+    }
+
+    while (ghostDists.values.toArray.distinct.length != 1) {
+      val minimum: (Ghost, Long) = ghostDists.toArray.minBy(_._2)
+      ghostDists(minimum._1) = minimum._1.next()
+    }
+
+    val dists: Array[Long] = ghostDists.values.toArray
+
+    return dists(0)
+  }
+
+  def main(args: Array[String]): Unit = {
+    val solution: Long = solve("./res/day8/input1.txt")
+    println(solution)
+  }
+}

tests/day8/Puzzle2Test.scala

@@ -0,0 +1,9 @@
+package day8
+
+import org.scalatest.funsuite.AnyFunSuite
+
+class Puzzle2Test extends AnyFunSuite {
+  test("Puzzle2.solve") {
+    assert(Puzzle2.solve("tests_res/day8/input1.txt") == 6)
+  }
+}