Sudoku for beginners: the only three techniques you need
Most sudoku guides start with a dozen named patterns. In practice, three techniques solve every easy puzzle and most medium ones. Learn these before anything else.
1. Naked single
Pick an empty cell and ask which digits it can legally hold. If exactly one digit remains, write it in. That is the whole technique.
The trick is doing this systematically rather than by eye: work row by row, and for each empty cell cross out the digits already present in its row, column and box. Beginners usually stop at the first cell that looks easy; the reliable habit is to check every cell in a row before moving on.
2. Hidden single
This is the technique that unlocks most puzzles people get stuck on. Pick a digit — say 7 — and look at one box. If 7 can only legally go in one cell of that box, it goes there, even if that cell could also hold other digits.
In other words: naked single asks "what can go in this cell?", hidden single asks "where can this digit go?". Alternating between those two questions is 90% of solving.
3. Box-line reduction
Look at a row that needs a 4. In one of the boxes that row passes through, the only cells that can hold a 4 all sit on that same row. Then the 4 for that box must be on that row — which means no other cell in the row outside the box can be a 4.
This eliminates candidates rather than placing digits. It rarely gives you a number immediately, but it turns an impossible board into one full of naked singles.
How to practise
Set pencil marks on, and do not place a digit unless you can say which rule justifies it. Speed comes from pattern recognition, and pattern recognition comes from justifying every move out loud for the first ten puzzles.
If you get stuck for more than two minutes on an easy puzzle, you have almost certainly missed a hidden single. Scan for each digit 1–9 in turn across each box before trying anything more advanced.
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