我的NQueens isSafeMove（）函数不断返回false

Question

我的NQueens isSafeMove（）函数不断返回false，我无法弄清楚原因。我相信它可能与我的checkLeft，checkUpperDiag或checkLowerDiag有关，但我没有看到它们有什么问题。 isSafeMove检查是否是女王的任何可移动距离中的一块，如果有返回false，如果没有则返回true。

import java.awt.Point;
public class NQueensModel 
{
    private int myNumQueens;
    private boolean myBoard[][];
    private boolean mySolutionBoard [][];
    private String mySolutionBoardString [][];
    private int myNumSolutions;


NQueensModel(int nQueens)
{
    myNumQueens = nQueens;
    myBoard = new boolean [myNumQueens][myNumQueens];
    mySolutionBoard = new boolean [myNumQueens][myNumQueens];
    mySolutionBoardString = new String [myNumQueens][myNumQueens];
}

public boolean solvePuzzle()
{
    return solvePuzzle(0);
}

private boolean solvePuzzle(int ncolumn)
{
    if (ncolumn >= myNumQueens)
    {
        return true;
    }
    for(int i = 0; i < myNumQueens; i++)
    {
        if(this.isSafeMove(i, ncolumn) == true)
        {
            this.placeQueen(i, ncolumn);
            if(this.solvePuzzle(ncolumn + 1) == true)
            {
                return true;
            }
            this.removeQueen(i, ncolumn);
        }
    }
    return false;
}

public boolean isSafeMove(int row, int col)
{
    if(this.checkLeft(row, col) || this.checkUpperDiag(row, col)
            || this.checkLowerDiag(row, col) == true)
    {
        System.out.println("false");
        return false;
    }

    else 
    {
        System.out.println("true");
        return true;
    }
}

private boolean checkLeft(int row, int col)
{

    if(col >= myNumQueens || row >= myNumQueens)
    {
        return false;
    }
    if(row == 0)
    {
        return true;
    }
    for(int i= col - 1 ; i >= 0; i--)
    {
        if(myBoard[row][i] == true)
        {
            return false;
        }
        if(i == 0)
        {
            return true;
        }
    }
    return false;
}

private boolean checkUpperDiag(int row, int col)
{
    if(col == 0 || row == 0)
    {
        return true;
    }
    for(int i = row, j = col; row >= 0 || col >= 0; row--, col--)
    {
        if(myBoard[row][col] == true)
        {
            return false;
        }
        if(col == 0 && row == 0)
        {
            return true;
        }
    }
    return false;
}

private boolean checkLowerDiag(int row, int col)
{
    if(col == 0 || row == myNumQueens - 1)
    {
        return true;
    }
    for(int i = row, j = col; row < myNumQueens || col < myNumQueens; row--, col++)
    {
        if(myBoard[row][col] == true)
        {
            return false;
        }
        if(col == 0 && row == myNumQueens - 1)
        {
            return true;
        }
    }

    return false;
}



public boolean placeQueen(int row, int col)
{
    if(myBoard[row][col] == false)
    {
        myBoard[row][col] = true;
        return false;
    }
    return false;
}


public String getMySolutionBoardString()
{
    for(int col = 0; col < myNumQueens; col++)
    {
        for(int row = 0; row < myNumQueens; row++)
        {
            if(myBoard[col][row] == true)
            {
                mySolutionBoardString[row][col] = "Q";
            }
            else
            {
                mySolutionBoardString[row][col] = "-";
            }
            System.out.print(mySolutionBoardString[row][col] + " ");
        }
        System.out.println("");
    }
    return null;
}

private boolean removeQueen(int row, int col)
{
    myBoard[row][col] = false;
    return false;
}

public boolean getQueenOnBoard(Point point)
{
    return myBoard[(int)point.getX()][(int)point.getY()];
}

public String toString()
{
    String string = this.getMySolutionBoardString();
    return string;
}

}

Answer 1

在你的循环中

for(int i = 0; i < myNumQueens; i++)
{
    if(this.isSafeMove(i, ncolumn) == true)
    {
        this.placeQueen(i, ncolumn);
        if(this.solvePuzzle(ncolumn + 1) == true)
        {
            return true;
        }
        this.removeQueen(i, ncolumn);
    }
}

当你第一次调用isSafeMove（i，ncolumn）时想想它i = 0所以checkLeft将返回true并且在ncolumn = 0之后的每次迭代所以你对checkUpperDiag（）和checkLowerDiag（）的调用将返回true，所以那些方法每次都返回true意味着isSafeMove将在循环的每次迭代中返回false