Coverage Summary for Class: Area (day18p1)

 package day18p1
 
 import kotlin.math.absoluteValue
 
 fun String.lavaCapacity(): Int {
   val digPlan = toDigPlan()
   val digGrid = digPlan.dig()
   digGrid.digInterior()
   return digGrid.capacity()
 }
 
 fun String.toDigPlan(): DigPlan = DigPlan(
   lines().map { it.toStep() }.toList()
 )
 
 
 private val stepRegex = """([RLUD]) (\d+) \((#\w+)\)""".toRegex()
 
 fun String.toStep(): Step =
   stepRegex.matchEntire(this)!!.destructured
     .let { (direction, distance, colorCode) ->
       Step(
         direction = Direction.valueOf(direction),
         distance = distance.toInt(),
         colorCode = colorCode
       )
     }
 
 data class DigPlan(val steps: List<Step>) {
   val lengthByDirection = steps.groupBy { it.direction }.mapValues { (_, steps) -> steps.sumOf { it.distance } }
   fun toText(): String = steps.joinToString("\n")
   fun length(): Int = steps.sumOf { it.distance }
 
   fun isLoop(): Boolean =
     lengthByDirection[Direction.R] == lengthByDirection[Direction.L] &&
       lengthByDirection[Direction.U] == lengthByDirection[Direction.D]
 
   fun rows(): Indexes {
     var max = 0
     var current = 0
     var min = 0
     for (step in steps) {
       when (step.direction) {
         Direction.D -> {
           current += step.distance
           max = max.coerceAtLeast(current)
         }
 
         Direction.U -> {
           current -= step.distance
           min = min.coerceAtMost(current)
         }
 
         else -> continue
       }
     }
     return Indexes(max, min)
   }
 
   fun columns(): Indexes {
     var max = 0
     var current = 0
     var min = 0
     for (step in steps) {
       when (step.direction) {
         Direction.R -> {
           current += step.distance
           max = max.coerceAtLeast(current)
         }
 
         Direction.L -> {
           current -= step.distance
           min = min.coerceAtMost(current)
         }
 
         else -> continue
       }
     }
     return Indexes(max, min)
   }
 
   data class Indexes(val max: Int, val min: Int) {
     val total: Int = max - min + 1
   }
 
   fun dig(): DigGrid {
     val rows = rows()
     val columns = columns()
     val digGrid = DigGrid((0 until rows.total).map { (0 until columns.total).map { Area.Terrain }.toMutableList() })
     var currentRow = rows.min.absoluteValue
     var currentCol = columns.min.absoluteValue
     digGrid.grid[currentRow][currentCol] = Area.Trench
     for (step in steps) {
       repeat(step.distance) {
         val (nextRow, nextColumn) = step.direction.next(currentRow, currentCol)
         require(nextRow >= 0) { "row $nextRow must be >= 0, $step / $it" }
         require(nextColumn >= 0) { "column $nextColumn must be >= 0, $step / $it" }
         digGrid.grid[nextRow][nextColumn] = Area.Trench
         currentRow = nextRow
         currentCol = nextColumn
       }
     }
     return digGrid
   }
 }
 
 data class DigGrid(val grid: List<MutableList<Area>>) {
   fun toText(): String = grid.joinToString("\n") { row -> row.joinToString("") { it.sign.toString() } }
   fun capacity(): Int = grid.asSequence().flatten().count { it == Area.Trench }
 
   fun digInterior() {
     val outsideAreas = mutableSetOf<Pair<Int, Int>>()
     for (row in grid.indices) {
       for (col in grid[row].indices) {
         if (grid[row][col] == Area.Trench || outsideAreas.contains(row to col)) {
           continue
         }
         outsideAreas.addAll(floodFill(row, col))
       }
     }
   }
 
   fun floodFill(startRow: Int, startCol: Int): Set<Pair<Int, Int>> {
     require(grid[startRow][startCol] == Area.Terrain)
     var inside = true
     val toVisit = mutableSetOf(startRow to startCol)
     val visited = mutableSetOf<Pair<Int, Int>>()
     while (toVisit.isNotEmpty()) {
       val (row, col) = toVisit.iterator().let {
         val pair = it.next()
         it.remove()
         pair
       }
       if (row == 0 || col == 0 || row == grid.size - 1 || col == grid[row].size - 1) {
         inside = false
       }
       visited.add(row to col)
       sequenceOf(
         row to col + 1,
         row + 1 to col,
         row to col - 1,
         row - 1 to col
       ).forEach { pair ->
         if (visited.contains(pair)) {
           return@forEach
         }
         val (r, c) = pair
         if (r < 0 || c < 0 || r >= grid.size || c >= grid[row].size) {
           return@forEach
         }
         if (grid[r][c] == Area.Trench) {
           return@forEach
         }
 
         toVisit.add(pair)
       }
     }
 
     if (inside) {
       visited.forEach { (row, col) -> grid[row][col] = Area.Trench }
       return emptySet()
     }
 
     return visited
   }
 }
 
 enum class Area(val sign: Char) {
   Trench('#'),
   Terrain('.')
 }
 
 data class Step(val direction: Direction, val distance: Int, val colorCode: String) {
   override fun toString(): String = "$direction $distance ($colorCode)"
 }
 
 enum class Direction {
   R {
     override fun next(row: Int, col: Int): Pair<Int, Int> = row to col + 1
 
   },
   L {
     override fun next(row: Int, col: Int): Pair<Int, Int> = row to col - 1
 
   },
   U {
     override fun next(row: Int, col: Int): Pair<Int, Int> = row - 1 to col
 
   },
   D {
     override fun next(row: Int, col: Int): Pair<Int, Int> = row + 1 to col
   };
 
   abstract fun next(row: Int, col: Int): Pair<Int, Int>
 }