Coverage Summary for Class: CoordinateXY (day23p1)

 package day23p1
 
 data class CoordinateXY(val x: Int, val y: Int) {
   init {
     require(x >= 0 && y >= 0)
   }
 }
 
 fun String.toAccessibleMap(): AccessibleMap {
   val lines = lines()
   val maxY = lines.size - 1
   val maxX = lines.first().length - 1
 
   fun Set<Pair<Int, Int>>.toNeighbours(coordinate: CoordinateXY): Sequence<CoordinateXY> =
     this.asSequence().map { (dx, dy) -> coordinate.x + dx to coordinate.y + dy }
       .filter { (x, y) -> x >= 0 && y >= 0 && x <= maxX && y <= maxY && lines[y][x] != '#' }
       .map { (x, y) -> CoordinateXY(x, y) }
 
 
   val tiles = lines.flatMapIndexed { y, line ->
     line.mapIndexedNotNull { x, tile ->
       val type = when (tile) {
         '.' -> TileType.Path
         '^' -> TileType.SlopeUp
         'v' -> TileType.SlopeDown
         '>' -> TileType.SlopeRight
         '<' -> TileType.SlopeLeft
         else -> return@mapIndexedNotNull null
       }
       val coordinate = CoordinateXY(x, y)
       if (type != TileType.Path) {
         val neighbours = setOf(-1 to 0, 1 to 0, 0 to -1, 0 to 1).toNeighbours(coordinate)
         require(neighbours.count() == 2)
       }
       val incoming = type.incomingDeltas.toNeighbours(coordinate).map { Path(it, coordinate) }.toSet()
       val outgoing = type.outgoingDeltas.toNeighbours(coordinate).map { Path(coordinate, it) }.toSet()
       Tile(coordinate, type, incoming, outgoing)
     }
   }.associateBy { it.coordinate }
 
   return AccessibleMap(
     tiles.mapValues { (_, tile) ->
       tile.copy(
         incoming = tile.incoming.filter { path -> tiles.getValue(path.from).outgoing.contains(path) }.toSet(),
         outgoing = tile.outgoing.filter { path -> tiles.getValue(path.to).incoming.contains(path) }.toSet()
       )
     },
     lines.first().withIndex().single { it.value == '.' }.let { CoordinateXY(it.index, 0) },
     lines.withIndex().last().let { (i, line) ->
       CoordinateXY(line.withIndex().single { it.value == '.' }.index, i)
     }
   )
 }
 
 data class AccessibleMap(val map: Map<CoordinateXY, Tile>, val start: CoordinateXY, val end: CoordinateXY) {
 
   init {
     map.values.forEach { tile ->
       require(tile.isStart() || tile.incoming.isNotEmpty())
       require(tile.isEnd() || tile.outgoing.isNotEmpty())
 
       tile.incoming.forEach { path ->
         require(map.getValue(path.from).outgoing.contains(path))
       }
       tile.outgoing.forEach { path ->
         require(map.getValue(path.to).incoming.contains(path))
       }
     }
   }
 
   private fun Tile.isStart() = coordinate == start
   private fun Tile.isEnd() = coordinate == end
 
   private fun Tile.isImportant() = isStart() || isEnd() || isCrossroads()
 
   fun isImportantTile(tile: Tile) = tile.isImportant()
 
   fun keepImportantOnly(): AccessibleMap {
     val important = map.values.asSequence()
       .filter { it.isImportant() }
       .toSet()
     val importantCoordinates = important.map { it.coordinate }.toSet()
 
     val incoming: Map<CoordinateXY, MutableSet<Path>> =
       important.asSequence().map { tile ->
         tile.coordinate to tile.incoming.asSequence().filter { importantCoordinates.contains(it.from) }.toMutableSet()
       }.toMap()
     val outgoing: Map<CoordinateXY, Set<Path>> = important.asSequence()
       .map { tile ->
         val coordinate = tile.coordinate
         val outgoingPaths = tile.outgoing
         coordinate to outgoingPaths.asSequence().mapNotNull path@{ p ->
           var current = map.getValue(p.to)
           var oldPath = p
           var length = 1
           while (!current.isImportant()) {
             oldPath = current.outgoing.asSequence().filter { it.to != oldPath.from }.singleOrNull() ?: return@path null
             current = map.getValue(oldPath.to)
             length++
           }
           if (length == 1) return@path p
 
           val newPath = Path(coordinate, current.coordinate, length)
 
           val endTile = incoming.getValue(current.coordinate)
           endTile.remove(oldPath)
           endTile.add(newPath)
 
           newPath
         }.toSet()
       }.toMap()
 
     return AccessibleMap(
       important.asSequence().map { tile ->
         tile.coordinate to tile.copy(
           incoming = incoming.getValue(tile.coordinate),
           outgoing = outgoing.getValue(tile.coordinate)
         )
       }.toMap(),
       start,
       end
     )
 
   }
 
   fun findLengthOfLongestHike(): Int {
     val start = map.getValue(start)
     val end = map.getValue(end)
     var max = 0
     hike(setOf(start), end) { _, length -> max = maxOf(max, length) }
     return max
   }
 
   private fun hike(hike: Set<Tile>, end: Tile, length: Int = 0, onSuccess: (Set<Tile>, Int) -> Unit) {
     val previous = hike.last()
     if (previous == end) onSuccess(hike, length)
 
     previous.outgoing.forEach { p ->
       val next = map.getValue(p.to)
       if (!hike.any { it.coordinate == next.coordinate }) hike(hike + next, end, length + p.length, onSuccess)
     }
   }
 }
 
 data class Tile(val coordinate: CoordinateXY, val type: TileType, val incoming: Set<Path>, val outgoing: Set<Path>) {
   fun isCrossroads() =
     (incoming.asSequence().map { it.from } + outgoing.asSequence().map { it.to }).distinct().count() > 2
 }
 
 data class Path(val from: CoordinateXY, val to: CoordinateXY, val length: Int = 1)
 
 enum class TileType(val incomingDeltas: Set<Pair<Int, Int>>, val outgoingDeltas: Set<Pair<Int, Int>> = incomingDeltas) {
   Path(setOf(-1 to 0, 1 to 0, 0 to -1, 0 to 1)),
   SlopeLeft(setOf(1 to 0), setOf(-1 to 0)),
   SlopeRight(setOf(-1 to 0), setOf(1 to 0)),
   SlopeUp(setOf(0 to 1), setOf(0 to -1)),
   SlopeDown(setOf(0 to -1), setOf(0 to 1))
 }