将 var 变量更改为 val

Question

我有这段代码

object Sudoku extends SudokuLikeGame {
  type T = Board

  def parse(str: String): Board = { 
      // helper method to filter out whether or not the coordinate given is mapped for one 
      // value and then must check for the rest of the peers
      def parseHelper(board: Map[(Int, Int), List[Int]], 
                      row: Int, col: Int): Map[(Int, Int), List[Int]] = {
        var parseBoard = board
        val oldValues = parseBoard(row, col).head//takes the first value 
        for(r <- 0 to 8; c <- 0 to 8){
          //iterates the list of peers from peers() and if at the row and col has a value 
          //contained within the board passed in
          for {(r, c) <- Solution.peers(row, col)
               if (parseBoard(r, c).contains(oldValues))} { 
            //removes all the old values from 
            val newValue = parseBoard(r, c) diff List(oldValues)
            //removes all the old values at the coord r, c and maps it to the correct value
            parseBoard = (parseBoard - ((r, c))) + ((r, c) -> newValue) 
            if(newValue.size == 1)  //one value means no more peers
              parseBoard = parseHelper(board, r, c)  
        }
      }
      parseBoard
    }

    var sudokuBoard = Map[(Int, Int), List[Int]]()
    if(str.length == 81){
      str
    }
    else{
      println("insuffient length")
      System.exit(1)
    }

我写了一些var变量。我知道这些是可变变量。但是，我被告知我不能在我的作业中使用这些变量。似乎我不能简单地将它们更改为 val，因为 val 是一个不可变引用，我正在重新分配 var 的值。

那么我怎样才能将这些 var 变量更改为 val？如果我的代码是否需要重新考虑结构？

Answer 1

这应该可以做到（未经测试，因为我们从您的代码中遗漏了一些东西，并猜测 Solution.peers 做了什么）。我们没有修改 parseBoard，而是使用 foldLeft（两次）将新板传递给下一步

 def peers(row:Int, col:Int) = {
    val rs = for (r <- 0 to 8 if r != row) yield (r, col)
    val cs = for (c <- 0 to 8 if c != col) yield (row, c)
    rs ++ cs
    } 
  val cells = for (r <- 0 to 8; c <- 0 to 8)  yield (r,c)


def parseHelper(board: Map[(Int, Int), List[Int]],
              row: Int, col: Int): Map[(Int, Int), List[Int]] = {
  val oldValues = board((row, col)).head //takes the first value
  cells.foldLeft(board) {
  case (b1, (r, c)) =>
    //iterates the list of peers from peers() and if at the row and col has a value
    //contained within the board passed in
    peers(row, col).foldLeft(b1) {
      case (b, (r, c)) =>

        if (b((r, c)).contains(oldValues)) {
          //removes all the old values from
          val newValue = b((r, c)) diff List(oldValues)
          //removes all the old values at the coord r, c and maps it to the correct value
          if (newValue.size == 1) parseHelper(board, r, c) else b - ((r, c)) + ((r, c) -> newValue)
        } else b
    }
  }
}

将 var 变量更改为 val

Changing var variables to val

scala

var