When you find it hard to identify straightforward answers in Sudoku, then it is time to use candidate numbers. The candidate numbers help in filling out all the possibilities for each empty cell depending on the figures already present on the Sudoku grid.
If you’re solving Sudoku on paper, consider making notes with a pencil so you can easily erase them later. Alternatively, you could use a pen with very light pressure. Another option is to jot down small numbers in the corners of the cells to keep them unnoticeable for future reference.
When you are solving Sudoku on our website, you can utilize a special note feature by activating the ‘Pencil’ mode. It is necessary to accurately fill out candidate numbers because any mistakes can increase puzzle difficulty and consume more time. By writing down possible values in the empty cells using figures that are not there yet, you get a better view of the solution.
Image 1 is a Sudoku puzzle you are going to solve. Now focus on the 3×3 box highlighted with the purple frame as shown in image 2. Turn the ‘Pencil’ mode ON. Now write candidate or possible numbers in all the empty cells.
Once finished you can see that the numbers 5 and 7 are the possible numbers for the red frame. Since 7 appears once in the entire 3×3 box, it is the clear winner for the red frame. Also, numbers 5 and 6 are the possible numbers for the green frame and 6 is the clear winner since it appears once in the 3×3 box.
Candidate numbers help you identify where each digit should go besides allowing you to apply advanced Sudoku solving methods. These techniques largely depend on information that comes from candidate numbers thus simplifying one’s way through the puzzle.
For more strategies and lessons about solving Sudoku see the Tips section on our website. Also, download our free printable Sudoku puzzle books.