n Queens Java不适用于4 by 4

Question

我输入的n Queens版本似乎适用于除4x4板以外的所有输入。 它需要一个棋盘大小和一个1个女王的起始位置。 有什么原因不能解决该大小的问题？ 我尝试输入4 1 2，但无法正确创建电路板

import java.io.*;

public class nQueens {
public static int N;
public static int skipCol;
public static int permaRow;
public static void printSolution(int board[][]) {
    PrintWriter file = null;
    try {
        file = new PrintWriter("solution.txt");
        // Prints Board to solution.txt
        for (int i = 0; i < N; i++) {
            for (int j = 0; j < N; j++) {
                if (board[i][j] == 1) {
                    // If board = 1 then there is a Queen, 0 then empty
                    file.println((i + 1) + " " + (j + 1));
                }
            }
        }
        file.flush();
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

public static boolean isSafe(int board[][], int row, int col) {
    // Returns True if safe, returns False if not safe
    // Checks all columns in the row
    int i,j;
    for (i = 0; i < col; i++) {
        if (board[row][i] == 1) {
            return false;
        }
    }
    // Check Diagonals (upper then lower)
    for (i = row, j = col; i >= 0 && j >= 0; i--, j--) {
        if (board[i][j] == 1) {
            return false;
        }
    }
    for (i = row, j = col; j >= 0 && i < N; i++, j--) {
        if (board[i][j] == 1) {
            return false;
        }
    }
    return true;
}

public static boolean solveNQueensCol(int board[][], int col) {
    if (col >= N) { // Base Case, checks if all queens are placed
        return true;
    }
    if (col != skipCol) {
        for (int i = 0; i < N; i++) {
            if (isSafe(board, i, col)) {
                board[i][col] = 1; // Changes that board space to Queen

                if (solveNQueensCol(board, col + 1) == true) {
                    // Recursively places all the Queens onto the board
                    return true;
                }
                // If placing queen at i, col doesn't work, remove it
                board[i][col] = 0;
            }
        }
    } else {
        board[permaRow][skipCol] = 1; // One Preset Queen
        return solveNQueensCol(board,col+1);
    }
    return false;

}

public static boolean solveNQueens(int x, int y) {
    // Creates new board with size N
    int board[][] = new int[N][N];
    for (int i = 0; i < N; i++) { // Fills board with 0s
        for (int j = 0; j < N; j++) {
            board[i][j] = 0;
        }
    }
    permaRow = x;
    skipCol = y;
    if (solveNQueensCol(board, 0) == false) {
        PrintWriter file = null;
        try {
            file = new PrintWriter("solution.txt");
            // Prints Board to solution.txt
            for (int i = 0; i < N; i++) {
                for (int j = 0; j < N; j++) {
                    if (board[i][j] == 1) {
                        // If board = 1 then there is a Queen, 0 then empty
                        file.println((i + 1) + " " + (j + 1));
                    }
                }
            }
            file.flush();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return false;
    }
    printSolution(board);
    return true;
}

public static void main(String[] args) {
    N = Integer.parseInt(args[0]);
    solveNQueens(Integer.parseInt(args[1]) - 1, Integer.parseInt(args[2]) - 1);
}

}

Answer 1

如果行和列的计数是从0到3，则当女王在1,2位开始时没有任何解决方案。