Sudoku Tips and Solving Techniques
Learn the techniques in this order. Each one unlocks the next difficulty level.
1. Scanning
Pick a digit and look at which rows and columns already contain it. Often a box has only one cell left where that digit can go.
2. Naked singles
If a cell has only one possible digit after crossing out everything in its row, column and box, write it in.
3. Hidden singles
If a digit can go into only one cell of a row, column or box, it belongs there, even when that cell has other candidates.
4. Pencil notes
Write small candidate digits in empty cells. Notes make pairs and patterns visible. Use the Notes button in the game.
5. Locked candidates
If a digit inside a box can only be in one row, it cannot appear in the rest of that row outside the box. The same works for columns and in reverse.
6. Naked pairs
Two cells in a row, column or box that share the same two candidates must hold those two digits, so remove them from the other cells of that unit.
7. X-Wing
If a digit appears in exactly two cells in each of two rows, and they line up in the same two columns, remove that digit from the rest of those columns.