Sudoku Solving Techniques
Every sudoku has exactly one solution that pure logic can reach, so a good solve never needs a guess. The trick is knowing which technique to reach for. Here are the methods that will carry you from a gentle grid to a genuinely hard one, roughly in the order you should try them.
1. Scanning (cross-hatching)
Start with the digit that appears most often. For each box still missing it, look along the rows and columns that already contain that digit — they "cross out" cells where it cannot go. If only one cell in the box survives, that is where the digit belongs. Scanning alone solves most of an easy sudoku.
2. The lone single
Work cell by cell and ask which digits are still allowed by that cell's row, column, and box. When only one candidate remains, you have a lone single — fill it in. Each one you place removes candidates elsewhere, often unlocking the next.
3. The hidden single
Sometimes a cell has several candidates, yet one of those digits has nowhere else to go in its row, column, or box. That is a hidden single: the digit is forced even though the cell looks undecided. Hidden singles are the workhorse of a medium grid.
4. Naked and pointing pairs
When two cells in a unit share the same two candidates and nothing else, those two digits are locked to that pair — you can erase them from every other cell in the unit. A related idea, the pointing pair, is when a box confines a digit to one row or column, letting you remove it further along that line. These pencil-mark techniques are what crack a hard sudoku.
Practice
Pick up these habits in order and you will rarely get stuck. Try them on the free sudoku maker — generate a fresh grid, solve on screen, and download a print-ready PDF with the answer key whenever you want to check your work.