Question

我试图制作一个程序来解决八皇后问题但我每次运行代码时都会遇到异常错误这就是我所拥有的。我有点困惑怎么办。任何对这个方向的帮助都将不胜感激。

线程“main”中的异常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

在'isUnderAttack（）'的循环中，这不好：

board[row-column+y][y]
board[row+column-y][y]

当'y'从'0'变为'board size'时，它将意味着索引超出了数组的范围（除非row和column都是0） - 正如错误信息明确说明的那样。

应使用适当的索引更正循环，或者通过添加条件来检查索引是否在边界内：

int rowIndex = row-column+y;
if(rowIndex>=0 && rowIndex<BOARD_SIZE) {
      if(board[row-column+y][y] == QUEEN) {
            return true;
      }
}

当然对于另一条对角线也一样......

_{该死的，在Android手机上键入代码很慢，即使是qwerty ......}

Answer 2

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;
}

Answer 3

其中任何一个的价值都低于零

row-column+y
row+column-y

Answer 4

导致错误的一种情景考虑这种情况，董事会[row + column-y] [y] == QUEEN 假设row = 1，column = 0且y为4，索引变为-ve，导致错误

八皇后Java异常错误

4 个答案: