public class QueensProblem {

    public static void main(String[] args) {
        //Initialisiere Schachfeld 8x8
        boolean[][] queen = new boolean[8][8];
        int counter = solutions(queen, 0);
        System.out.println(counter);
    }

    private static int solutions(boolean[][] queen, int row) {
        if (row == queen.length) {
            return 1;
        }

        int counter = 0;
        for (int col = 0; col < queen.length; col++) {
            if (!isPositionSave(queen, row, col)) {
                continue;
            }

            queen[row][col] = true;
            counter += solutions(queen, row + 1);
            queen[row][col] = false;
        }

        return counter;
    }

    public static boolean isPositionSave(boolean[][] queen, int row, int col) {

        for (int i = 0; i < row; i++) {
            int dC = row - i;
            // Teste Spalte
            if (queen[i][col]) {
                return false;
            }
            // Teste linke Diagonale
            if (col - dC >= 0 && queen[i][col - dC]) {
                return false;
            }
            // Teste rechte Diagonale
            if (col + dC < queen.length && queen[i][col + dC]) {
                return false;
            }
        }

        return true;
    }
}