Coverage Summary for Class: Coordinate2D (day22p2)

 package day22p2
 
 fun String.sumOfOtherBricksToFallInChainReactions(): Int =
   toSnapshot().settle().sumOfOtherBricksToFallInChainReactions()
 
 fun String.numberOfBricksThatCanBeDisintegrated(): Int = toSnapshot().settle().numberOfBricksThatCanBeDisintegrated()
 
 fun String.toSnapshot(): Snapshot = Snapshot(
   this
     .lineSequence()
     .map { line -> line.split("~").map { it.split(",").map { n -> n.toInt() } } }
     .mapIndexed { index, parts ->
       Brick(index + 1, parts[0][0], parts[0][1], parts[0][2], parts[1][0], parts[1][1], parts[1][2])
     }
     .associateBy { it.id }
 )
 
 data class Snapshot(val bricks: Map<BrickId, Brick>) {
   constructor(vararg bricks: Brick) : this(bricks.associateBy { it.id })
 
   val maxX: Int = bricks.values.maxOf { it.end.x }
   val maxY: Int = bricks.values.maxOf { it.end.y }
   val maxZ: Int = bricks.values.maxOf { it.end.z }
 
   fun settle(): Snapshot {
 
     val bricksByMinZ = bricks.values.asSequence().sortedBy { it.start.z }.toMutableList()
 
     val topDownXYView: MutableMap<Coordinate2D, Pair<Int, Brick>?> =
       (0..maxX).flatMap { x -> (0..maxY).asSequence().map { y -> Coordinate2D(x, y) to null } }
         .toMap(mutableMapOf())
 
     val settledBricks = mutableListOf<Brick>()
 
     while (bricksByMinZ.isNotEmpty()) {
       val current = bricksByMinZ.removeFirst()
       val supporterCandidates = current.xyCoordinates().mapNotNull { topDownXYView[it] }
 
       val (supporterZ, supporters) = supporterCandidates.maxOfOrNull { it.first }?.let { max ->
         max to supporterCandidates.asSequence().filter { it.first == max }.map { it.second.id }.toSet()
       } ?: (0 to emptySet())
 
       val updated = current.copy(
         start = current.start.copy(z = supporterZ + 1),
         end = current.end.copy(z = supporterZ + 1 + current.end.z - current.start.z),
         supporters = supporters
       )
 
       settledBricks.add(updated)
 
       updated.xyCoordinates().forEach { xy -> topDownXYView[xy] = updated.end.z to updated }
     }
 
     return Snapshot(settledBricks.associateBy { it.id })
   }
 
   fun bricksThatCanBeDisintegrated(): Set<BrickId> {
     val result = bricks.keys.toMutableSet()
     bricks.values.forEach { brick ->
       if (brick.supporters.size == 1) {
         result.remove(brick.supporters.single())
       }
     }
     return result
   }
 
   fun numberOfBricksThatCanBeDisintegrated(): Int = bricksThatCanBeDisintegrated().size
   fun sumOfOtherBricksToFallInChainReactions(): Int {
     val chainReactionStarters =
       bricks.values.asSequence().filter { it.supporters.size == 1 }.map { it.supporters.single() }.toSet()
 
     return chainReactionStarters.sumOf { numOfOtherBricksToFallInChainReaction(it) }
   }
 
   private fun numOfOtherBricksToFallInChainReaction(id: BrickId): Int {
     val supporterToSupportedsMap: Map<BrickId, Set<BrickId>> = bricks.values
       .flatMap { supported -> supported.supporters.map { it to supported.id } }
       .groupingBy { it.first }
       .fold(emptySet()) { set, pair -> set + pair.second }
 
     val supportedToSupportersMap: Map<BrickId, MutableSet<BrickId>> = supporterToSupportedsMap.asSequence()
       .flatMap { (supporter, supporteds) -> supporteds.map { it to supporter } }
       .groupingBy { it.first }
       .fold(emptySet<BrickId>()) { set, pair -> set + pair.second }
       .mapValues { it.value.toMutableSet() }
 
     val disintegratedBricks = mutableListOf(id)
     var disintegratedCount = 0
     while (disintegratedBricks.isNotEmpty()) {
       val current = disintegratedBricks.removeFirst()
       supporterToSupportedsMap[current]?.forEach { supported ->
         val supporters = supportedToSupportersMap.getValue(supported)
         supporters.remove(current)
         if (supporters.isEmpty()) {
           disintegratedBricks.add(supported)
           disintegratedCount++
         }
       }
     }
     return disintegratedCount
   }
 }
 
 data class BrickId(val id: Int)
 
 data class Brick(
   val id: BrickId,
   val start: Coordinate3D,
   val end: Coordinate3D,
   val supporters: Set<BrickId> = emptySet()
 ) {
 
   constructor(id: Int, sx: Int, sy: Int, sz: Int, ex: Int, ey: Int, ez: Int, vararg supporters: Int) : this(
     BrickId(id),
     Coordinate3D(sx, sy, sz),
     Coordinate3D(ex, ey, ez),
     supporters.asSequence().map { BrickId(it) }.toSet()
   )
 
   init {
     require(start.x <= end.x)
     require(start.y <= end.y)
     require(start.z <= end.z)
     require(0 <= start.x)
     require(0 <= start.y)
     require(1 <= start.z)
   }
 
   fun xyCoordinates(): Set<Coordinate2D> =
     (start.x..end.x).flatMap { x -> (start.y..end.y).map { y -> Coordinate2D(x, y) } }.toSet()
 }
 
 data class Coordinate2D(val x: Int, val y: Int)
 
 data class Coordinate3D(val x: Int, val y: Int, val z: Int)