private boolean solveDFS(Integer[][] matrix, int i, int j) {
        if (i == dimension - 1 && j >= dimension) return true;
        if (j == dimension) {
            System.out.println(convertGameToShow(matrix));
            return solveDFS(matrix.clone(), i + 1, 0);
        }
        if (matrix[i][j] != -1) {
            return solveDFS(matrix.clone(), i, j + 1);
        } else {
            for (int num = 1; num <= dimension; num++) {
                Integer[][] aux = matrix.clone();
                aux[i][j] = num;
                if (check(aux, i, j)) {
                    matrix[i][j] = num;
                    if (solveDFS(matrix.clone(), i, j + 1)) {
                        gameMatrix = matrix;
                        return true;
                    }
                }
            }
            matrix[i][j] = -1;
        }
        return false;
    }

    public boolean check(Integer[][] game, int i, int j) {
        ArrayList<Integer> lineVal = new ArrayList<>();
        ArrayList<Integer> colVal = new ArrayList<>();
        for (int k = 0; k < dimension; k++) {
            if (game[i][k] != -1 && lineVal.contains(game[i][k]))
                return false;
            else lineVal.add(game[i][k]);

            if (game[k][j] != -1 && colVal.contains(game[k][j]))
                return false;
            else colVal.add(game[k][j]);
        }
        return true;
    }