public void computeCellsToSolve() {
        int cells = 0;
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 0; j++) {
                if (board[i][j].getValue() == 0) {
                    cells++;
                }
            }
        }
        cellsToSolve = cells;
    }