Sudoku Strategies: Singles, Pairs and Scanning
Scanning rows, columns and boxes
Start by selecting one digit, such as 7, and inspect the grid. In each 3 × 3 box, crossed-out rows and columns can reveal the only location where that digit may go. This is a systematic way to solve easier puzzles.
Naked singles
A naked single is a cell with only one possible digit after excluding numbers already present in its row, column and box. Write it down confidently and rescan the affected areas.
Hidden singles
A hidden single occurs when a digit can fit in only one cell of a row, column or box, even if that cell still has several pencil candidates. Look for where a particular digit can appear, not just how many choices each cell has.
Candidate pairs
If two cells in one row, column or box contain exactly the same two candidates, these digits are reserved for those cells. You may remove both candidates from other cells in that unit. Recheck all affected notes before going further.
Practice without guessing
Work one technique at a time and use notes to track your reasoning. If you are stuck, take a break and examine another part of the grid; the built-in hint remains optional.