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Sudoku Strategy: From Scanning to X-Wing
Every ThinkyPlay Sudoku has exactly one solution, and logic alone can find it. The trick is moving up a ladder of techniques as the board fills.
1. Scan before you place
Look at one box, one row or one column at a time and ask where each missing digit can go. A digit that can only live in one cell of a unit is a hidden single — place it immediately. Rescan the same unit after every placement, because filling a cell often unlocks its neighbours.
2. Keep pencil marks honest
Beyond Easy, write the candidates for each empty cell. Erase a candidate whenever a placement removes it from that cell. Pencil marks are only useful when they stay exact — a single stale mark sends you hunting for ghosts.
3. Naked and hidden pairs
When two cells in one unit share exactly the same two candidates, those digits are claimed — you can remove them from every other cell in the unit (a naked pair). The reverse also works: if two digits can only appear in two cells of a unit, those cells may hold nothing else (a hidden pair).
4. Row and column scanning
Pick a missing digit, say 7. Trace across every box it already appears in: each box’s 7 is confined to one row or column by its neighbours. That confinement often leaves exactly one cell in another box — a classic cross-hatching placement that requires no notes at all.
5. Pointing pairs and X-Wing
If all of a digit’s candidates inside a box share one row, that digit is impossible elsewhere on the row — erase it. The famous X-Wing appears when two rows both allow a digit in the same two columns; the digit then claims those columns, letting you remove it from other rows. Hard and Master boards lean on these patterns.
6. When you get stuck
Re-scan every box with fresh eyes rather than guessing. Genuine sudoku never needs a coin flip; a lucky guess also hides your mistakes for many moves. If you are still blocked, use the Hint button to reveal the exact logical next move, then figure out why it is forced.