Coverage Summary for Class: Coordinate (day21p2)

 package day21p2
 
 import day21p2.Field.GardenPlot
 import day21p2.Field.Rock
 
 fun String.expand(times: Int): String {
   if (times == 1) return this
   require(times % 2 == 1)
   val withoutS = replace("S", ".")
   val nonSRow = withoutS.lineSequence().map { it.repeat(times) }.joinToString("\n")
   val nonSHalfRow = withoutS.lineSequence().map { it.repeat(times / 2) }.joinToString("\n")
   val SRow = nonSHalfRow.lineSequence().zip(lineSequence()).map { (a, b) -> "$a$b$a" }.joinToString("\n")
 
   val nonSRowAllHalf = generateSequence { nonSRow }.take(times / 2).joinToString("\n")
 
   return nonSRowAllHalf + "\n" + SRow + "\n" + nonSRowAllHalf
 }
 
 fun String.numOfReachableGardenPlots(numOfSteps: Int): Int = toGardenMap().numOfReachableGardenPlots(numOfSteps)
 
 fun String.toGardenMap(): GardenMap = GardenMap(
   grid = lineSequence().map { line ->
     line.map {
       when (it) {
         '.' -> GardenPlot
         'S' -> GardenPlot
         else -> {
           require(it == '#')
           Rock
         }
       }
     }
   }.toList(),
   start = lineSequence().flatMapIndexed { row, line ->
     line.mapIndexedNotNull { col, c ->
       if (c == 'S') Coordinate(row, col) else null
     }
   }.single()
 )
 
 data class GardenMap(val grid: List<List<Field>>, val start: Coordinate) {
   val distanceGrid = calcDistanceGrid()
   fun distanceGridAsText(): String = distanceGrid.joinToString("\n") {
     it.joinToString(" ") { n ->
       (n?.toString() ?: "#").padStart(4, ' ')
     }
   }
 
   private fun calcDistanceGrid(): List<List<Int?>> {
     val distanceGrid: List<MutableList<Int?>> = grid.map { it.indices.map { null }.toMutableList() }
 
     distanceGrid[start.row][start.col] = 0
     val toBeVisited = mutableListOf(start)
     while (toBeVisited.isNotEmpty()) {
       val current = toBeVisited.removeFirst()
       val distance = distanceGrid[current.row][current.col]!! + 1
       sequenceOf(
         current.copy(row = current.row - 1),
         current.copy(row = current.row + 1),
         current.copy(col = current.col - 1),
         current.copy(col = current.col + 1)
       ).filter { (row, col) -> row in grid.indices && col in grid[row].indices }
         .filter { (row, col) -> grid[row][col] == GardenPlot }
         .filter { (row, col) -> distanceGrid[row][col] == null || distanceGrid[row][col]!! > distance }
         .forEach { next ->
           distanceGrid[next.row][next.col] = distance
           toBeVisited.add(next)
         }
     }
 
     return distanceGrid
   }
 
   fun possibleTargetsGridAsText(numOfSteps: Int): String =
     distanceGrid.asSequence().withIndex().joinToString("\n") { (row, ints) ->
       ints.withIndex().joinToString("") { (col, n) ->
         if (n == null) "#" else {
           val diff = numOfSteps - n
           if (diff >= 0 && diff % 2 == 0) "O" else if (start == Coordinate(row, col)) "S" else "."
         }
       }
     }
 
   fun numOfReachableGardenPlots(numOfSteps: Int): Int =
     distanceGrid.asSequence().flatMap { ints ->
       ints.asSequence().filter { n ->
         if (n == null) false else {
           val diff = numOfSteps - n
           diff >= 0 && diff % 2 == 0
         }
       }
     }.count()
 
   val gridSize = grid.size
   private val halfGridSize = gridSize / 2
 
   fun polynomialSteps(): Sequence<Int> {
     require(gridSize == grid.first().size)
     return generateSequence(0) { it + 1 }.map { halfGridSize + it * gridSize }
   }
 
   fun isPolynomialStep(n: Int): Boolean = (n - halfGridSize) % gridSize == 0
 }
 
 
 enum class Field {
   GardenPlot,
   Rock
 }
 
 data class Coordinate(val row: Int, val col: Int)