public class Queen {

private char[][] matrix;

private int size;

private int[] position;

private int result;

public int getResult() {

return result;

}

public Queen(int size) {

this.size = size;

matrix = new char[size][size];

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

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

matrix[i][j] = ‘x‘;

}

}

position = new int[size];

}

private void printMatrix() {

System.out.printf("---- sulution %d ----\n", result);

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

System.out.print("{");

for (int j = 0; j < size - 1; j++)

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

System.out.print(matrix[i][size - 1]);

System.out.println("}");

}

}

private boolean isValid(int row, int col) {

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

if (position[i] == position[row]) {

return false;

}

if (Math.abs(position[i] - position[row]) == row - i) {

return false;

}

}

return true;

}

public void trial(int row) {

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

matrix[row][i] = ‘.‘;

position[row] = i;

if (isValid(row, position[row])) {

if (row < size - 1) {

trial(row + 1);

} else {

/* success */

result++;

printMatrix();

}

}

matrix[row][i] = ‘x‘;

}

}

public static void main(String[] args) {

Queen test = new Queen(4);

test.trial(0);

System.out.printf("result is: %d", test.getResult());

}

}