Sudoku-YFoundations
Stuck in Sudoku? A short route before guessing
Being stuck does not automatically mean you need the most advanced technique. Try changing the question you ask of the board.
Check your starting information
Look for conflicting values or missing notes first. Revisit recently changed units. A newly placed 8 affects its row, column and box; those are useful places to begin instead of scanning the entire grid without a focus.
Alternate between cells and digits
Ask what each cell can contain, then ask where each missing digit can go. In our example row A needs {2,5,7}, with A1={2,7}, A4={2,5}, A8={2,5}. Every cell has two notes, yet only A1 can take 7. Switching from a cell view to a digit view reveals a move.
Expand the search gradually
Try pairs and locked candidates after singles, then consider harder patterns. This is our suggested learning route, not a compulsory solving order. If you use a hint, study one move and explain its evidence before asking for the next. Memorising its answer alone will not show why the elimination worked.
Give an assumption a return point
Keep the earlier state and distinguish conditional eliminations. A contradiction rejects a case; merely finding no problem yet does not confirm it. Taking a break or practising a simpler example is also a reasonable next step.
Try before looking
Try before revealing
Does the example have a placement despite every empty cell having two candidates?
Show explanation
Yes: A1=7, a Hidden Single. The absence of single-candidate cells does not require guessing.
References and further reading
Read the source explanations and compare them with our examples. Links are references, not endorsements or claims of affiliation.