Two Sudoku strategies to try first

A good first strategy is to look for a choice that has become certain. You can find one by studying a cell or by studying where a number can go within a group.

These two approaches are often called naked singles and hidden singles. Both follow directly from the standard Sudoku rules.

Find a cell with one candidate

For a naked single, check an empty cell’s row, column, and box. Rule out the digits already in those groups. If only one number remains, that is the answer for the cell.

In our practice puzzle, the center cell is a useful example. Row 5 allows 2, 5, 6, 7, and 9. Column 5 rules out all of those except 5, and the center box also allows 5. You can enter 5 with no guesswork.

The first-move walkthrough explains that scan step by step. Sudoku.com also describes this technique as an obvious single.

Find a number with one possible home

For a hidden single, choose a row, column, or box and ask where a missing number could go. If just one cell allows it, place the number there, even if that cell has other candidates.

Here is a small, separate example. A row has three empty cells and is missing 2, 5, and 9. Their candidate lists are as follows.

Only the second cell can contain 5. Place 5 there. You still need more information to decide where 2 and 9 belong.

Sudoku.com’s hidden-single explanation describes the same idea. If you use notes to find this pattern, make sure the candidate lists for the whole group are complete.

Repeat after each move

A placement changes the candidates in its row, column, and box. Recheck those areas before starting a new scan of the whole board. Update any notes you have written.

Know when to pause

If neither technique gives you a move, it does not mean the puzzle is broken. Harder puzzles can require other techniques. Review your notes, try another part of the board, or use an explanation-based hint in a released app.

For a first puzzle, practice finding certain moves and understanding why they work. Speed can wait.