N Queens

I/P: 4

O/P:

0-1, 1-3, 2-0, 3-2, . 0-2, 1-0, 2-3, 3-1, .

package pep.Day12;

public class N_Queens {
    public static void main(String[] args) throws Exception {
        int[][] chess = new int[4][4];
        printNQueens(chess, "", 0);
    }


    public static void printNQueens(int[][] chess, String qsf, int row) {
        if (row == chess.length) {
            System.out.println(qsf + ".");
            return;
        }

        for (int col = 0; col < chess.length; col++) {
            if (isSafePlaceForTheQueen(chess, row, col)) {
                chess[row][col] = 1;
                printNQueens(chess, (qsf + row + "-" + col + ", "), row + 1);
                chess[row][col] = 0;
            }
        }
    }

    private static boolean isSafePlaceForTheQueen(int[][] chess, int row, int col) {
        for (int i = 0; i < row; i++) {
            for (int j = 0; j < chess[0].length; j++) {
                // right diagonal, left diagonal
                if (((i + j == row + col) || (i - j == row - col)) && chess[i][j] == 1)
                    return false;

                // upwards
                if (chess[i][col] == 1)
                    return false;
            }
        }
        return true;
    }
}

private static boolean isSafePlaceForTheQueen(int[][] chess, int row, int col) {
    // upwards
    for (int i = row - 1, j = col; i >= 0; i--)
        if (chess[i][j] == 1)
            return false;

    // left diagonal
    for (int i = row - 1, j = col - 1; i >= 0 && j >= 0; i--, j--)
        if (chess[i][j] == 1)
            return false;

    // right diagonal
    for (int i = row - 1, j = col + 1; i >= 0 && j < chess.length; i--, j++)
        if (chess[i][j] == 1)
            return false;

    return true;
}