public static void nqueen(char board[][], int row) {

if (row == board.length) {

printBoard(board);

return;

}

for (int j = 0; j < board.length; j++) {

if (isSafe(board, row, j)) {

board[row][j] = 'Q';

nqueen(board, row + 1);

board[row][j] = 'X';

}

}

}

public static boolean isSafe(char board[][], int row, int col) {

// Vertical Up

for (int i = row - 1; i >= 0; i--) {

if (board[i][col] == 'Q') {

return false;

}

}

// Diagonal left Up

for (int i = row - 1, j = col - 1; i >= 0 && j >= 0; i--, j--) {

if (board[i][j] == 'Q') {

return false;

}

}

// Diagonal right up

for (int i = row - 1, j = col + 1; i >= 0 && j < board.length; i--, j++) {

if (board[i][j] == 'Q') {

return false;

}

}

return true;

}

public static void printBoard(char[][] board) {

System.out.println("----------------");

for (char row[] : board) {

for (char element : row) {

System.out.print(element + " ");

}

System.out.println();

}

}

// Time Complexity:O(n!)

public static void main(String args[]) {

int n = 4;

char board[][] = new char[n][n];

for (int i = 0; i < n; i++) {

for (int j = 0; j < n; j++) {

board[i][j] = 'X';

}

}

// Solve the N-Queens problem

nqueen(board, 0);

}