BEFORE ANYTHING ELSE
Three rules. Every row, every column, and every 3×3 box must contain each digit 1 through 9 exactly once. That's it. Everything below is just a faster way to apply those three rules.
One more thing: a real Sudoku has exactly one solution and you can reach it without guessing. If you find yourself guessing, back up — you missed something.
1. NAKED SINGLES
A cell where only one digit is possible — every other digit already appears in that row, column, or box.
Pencil-mark candidates if it helps. When a cell has one candidate left, place it. Easy puzzles often unravel from one naked single triggering another.
Spend more time scanning than solving. Most beginners miss singles because they're not looking for them — they're looking for "the answer".
2. HIDDEN SINGLES
A digit that can only go in one cell within a row, column, or box — even if that cell has several candidates.
Pick a digit (try 1 first). Look at every row, column, and box. If the digit fits in only one cell of any of those units, place it. Walk through 1 through 9 in order — most easy boards have several hidden singles waiting.
3. POINTING PAIRS AND TRIPLES
Inside one 3×3 box, all candidates for a digit fall in the same row (or column). That digit can't appear elsewhere in that row — so you can eliminate it from the rest of the row.
It doesn't place a digit directly. It thins the candidates somewhere else, which usually triggers a naked or hidden single nearby.
4. NAKED PAIRS
Two cells in the same row, column, or box that both have exactly the same two candidates. Those two digits are locked into those two cells — you can remove them from every other candidate list in the same unit.
Naked triples work the same way with three cells sharing three candidates. The same logic scales up; you'll rarely need quads in a beginner puzzle.
WHEN TO USE WHICH
Use them in this order, every time:
- Scan for naked singles.
- Walk 1–9 looking for hidden singles in every unit.
- If you're stuck, pencil-mark candidates.
- Look for pointing pairs and naked pairs to prune.
- Go back to step 1 — pruning almost always unlocks new singles.
This loop solves easy and medium Sudokus reliably. If a puzzle resists all four techniques, it's a hard one and you'll need x-wings, colouring, or chain logic — a separate guide.
ONE LAST THING
Speed comes from scanning, not memorisation. Practised solvers see naked and hidden singles without consciously thinking. The only way to get there is to solve a lot of easy puzzles before you move up — which is why GridJoy keeps every difficulty tier unlocked from day one.