java - 八皇后Java异常错误

Question

我试图编写一个程序来解决八皇后区问题，但每次运行代码时我都会收到异常错误，这就是我所拥有的。我对做什么有点困惑。对方向的任何帮助将不胜感激。

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException:-1 at Queens.isUnderAttack(Queens.java:132) at Queens.placeQueens(Queens.java:78) at Queens.main(Queens.java:155)

public class Queens
{
    //squares per row or column
    public static final int BOARD_SIZE = 8;

    //used to indicate an empty square 
    public static final int EMPTY = 0;

    //used to indicate square contains a queen
    public static final int QUEEN = 1;

    private int board[][]; //chess board

    public Queens()
    {
        //constructor: Creates an empty square board.
        board = new int[BOARD_SIZE][BOARD_SIZE];

    }


    //clears the board
    //Precondition: None
    //Postcondition: Sets all squares to EMPTY
    public void clearBoard()
    {
        //loops through the rows
        for(int row = 0; row < BOARD_SIZE; row++)
        {
            //loops through the columns
            for (int column = 0; column < BOARD_SIZE; column++)
            {
                board[row][column] = EMPTY;
            }
        }   
    }


    //Displays the board 
    //precondition: None
    //postcondition: Board is written to standard output; 
    //zero is an EMPTY square, one is a square containing a queen (QUEEN).
    public void displayBoard()
    {
        for (int row = 0; row < BOARD_SIZE; row++)
        {
            System.out.println("");

            for (int column = 0; column < BOARD_SIZE; column++)
            {
                System.out.print(board[row][column] + " ");
            }
        }
    }



    //Places queens in columns of the board beginning at the column specified.
    //Precondition: Queens are placed correctly in columns 1 through column-1.
    //Postcondition: If a solution is found, each column of the board contains one queen and
    //method returns true; otherwise, returns false (no solution exists for a queen anywhere in column specified).
    public boolean placeQueens(int column)
    {
        if(column >= BOARD_SIZE)
        {
            return true; //base case
        }
        else
        {
            boolean queenPlaced = false;
            int row = 1; // number of square in column

            while( !queenPlaced && (row < BOARD_SIZE))
            {
                //if square can be attacked
                **if (!isUnderAttack(row, column))**
                {
                    setQueen(row, column); //consider next square in column
                    queenPlaced = placeQueens(column+1);
                    //if no queen is possible in next column,
                    if(!queenPlaced)
                    {
                        //backtrack: remover queen placed earlier
                        //and try next square in column
                        removeQueen(row, column);
                        //++row;
                    }
                }
                row++;
            }
            return queenPlaced;
        }

    }



    //Sets a queen at square indicated by row and column
    //Precondition: None
    //Postcondition: Sets the square on the board in a given row and column to Queen.
    private void setQueen(int row, int column)
    {
        board[row][column] = QUEEN; 
    }



    //removes a queen at square indicated by row and column
    //Precondition: None
    //Postcondition: Sets the square on the board in a given row and column to EMPTY.
    private void removeQueen(int row, int column)
    {
        board[row][column] = EMPTY;
    }


    //Determines whether the square on the board at a given row and column is
    //under attack by any queens in the columns 1 through column-1.
    //Precondition: Each column between 1 and column-1 has a queen paced in a square at
    //a specific row. None of these queens can be attacked by any other queen.
    //Postcondition: If the designated square is under attack, returns true: otherwise return false.
    private boolean isUnderAttack(int row, int column)
    {


            for (int y=0; y<BOARD_SIZE; y++)
            {
                if (board[row][y] == QUEEN ||    // possible horizontal attack
                        board[row-column+y][y] == QUEEN ||   // diagonal NW
                        **board[row+column-y][y] == QUEEN)     // diagonal SW**
                        return true;
            }

        return false;
    }



    private int index(int number)
    {
        //Returns the array index that corresponds to a row or column number.
        //Precondition: 1 <= number <= BOARD_SIZE.
        //Postcondition: Returns adjusted index value

        return number -1 ;
    }


    //main to test program
    public static void main(String[] args)
    {
        Queens Q = new Queens();
        **if(Q.placeQueens(0))**
        {
            System.out.println(Q);
        }
        else
        {
            System.out.println("Not Possible");
        }
    }


}

Answer 1

private boolean isUnderAttack(int row, int column)
{
    for (int y = 0; y < BOARD_SIZE; y++)
    {
        if (board[row][y] == QUEEN)
            return true; // possible horizontal attack

        int x1 = row - column + y;
        if (0 <= x1 && x1 < BOARD_SIZE && board[x1][y] == QUEEN)
            return true; // diagonal NW

        int x2 = row + column - y;
        if (0 <= x2 && x2 < BOARD_SIZE && board[x2][y] == QUEEN)
            return true; // diagonal SW
    }

    return false;
}