NQueens Counter Solution

NQueens-Solution.scala

// https://leetcode.com/problems/n-queens-ii/
object Solution extends App {
  def totalNQueens(N: Int): Int = {
    type Board = Array[Array[Boolean]]
    def putQueen(board: Board, row: Int, col: Int): Unit    = board(row)(col) = true
    def removeQueen(board: Board, row: Int, col: Int): Unit = board(row)(col) = false
    def isValid(board: Board, row: Int, col: Int): Boolean  = {
      val checkCol = (0 until row).forall(currRow => board(currRow)(col) == false )
      val checkLeftDiagonal = ((row to 0 by -1) zip (col to 0 by -1)).forall { case (currRow, currCol) => board(currRow)(currCol) == false }
      val checkRightDiagonal = ((row to 0 by -1) zip (col until N)).forall { case (currRow, currCol) => board(currRow)(currCol) == false }
      checkCol && checkLeftDiagonal && checkRightDiagonal
    }

    def countQueenPlacements(board: Board, row: Int)(soFarPlaces: Int): Int = {
      def isFinished = { soFarPlaces == N }
      if(isFinished) 1
      else {
        var solutions = 0
        (0 until N).foreach { col =>
          if(isValid(board, row, col)) {
            putQueen(board, row, col)
            solutions += countQueenPlacements(board, row + 1)(soFarPlaces + 1)
            removeQueen(board, row, col)
          }
        }
        solutions
      }
    }

    countQueenPlacements(Array.tabulate(N, N)((_, _) => false), 0)(0)
  }

  print(totalNQueens(8))
}