static int count = 0;

public static void main(String args[]) {

int n = 4;

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

int row = 0;

// initialize

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

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

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

}

}

// Find one solution

if (nQueenOne(board, row)) {

System.out.println("Solution is possible");

printBoard(board);

} else {

System.out.println("Solution is not possible");

}

// Count all solutions

count = 0; // reset

nQueenAll(board, 0);

System.out.println("Total number of boards for n queens: " + count);

}

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

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

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

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

System.out.print(board[i][j] + " ");

}

System.out.println();

}

}

// Find ONE solution

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

if (row == board.length) {

return true;

}

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

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

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

if (nQueenOne(board, row + 1)) {

return true;

}

board[row][j] = '.'; // backtrack

}

}

return false;

}

// Count ALL solutions

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

if (row == board.length) {

count++;

return;

}

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

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

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

nQueenAll(board, row + 1);

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

}

}

}

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

// column check

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

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

return false;

}

}

// left diagonal

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

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

return false;

}

}

// right diagonal

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

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

return false;

}

}

return true;

}