Stuck on a medium Sudoku? Stop guessing and find one fact
A harder grid may not have a nearly complete row. Do not choose the digit that looks most likely. Write the digits that can still fit in one empty cell. Each possible digit is called a candidate.
- ✓ Screenshot, photo, or typed grid
- ✓ One explained clue included
- ✓ No answer revealed
Definition
When a medium Sudoku stalls, update the possible digits in each empty cell and look for one forced placement.
When one cell has only one possible digit after you check its row, column, and 3×3 box, that digit is forced.
- 1. Choose one empty cellCheck its row, column, and 3×3 box.
- 2. Rule out the used digitsRow 1 contains 3, 5, and 6. Column 3 contains 2, 8, and 9. The top-left 3×3 box also contains 1 and 7. Together, these checks rule out every digit except 4.
- 3. Place the only candidateOnly candidate 4 remains, so 4 must go in the outlined cell. A cell with one candidate is called a naked single.
Row 1 rules out 3, 5, and 6. Column 3 rules out 2, 8, and 9. The top-left 3×3 box rules out 1 and 7. Only 4 remains.
A reference verified by Doku.su
Doku.su checks every placement or elimination in this example with its deterministic Sudoku engine. Illustrative candidates are labelled when they do not represent a complete puzzle state.
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