Learn · 2 min read
🔢 Sudoku Strategies: From Beginner to Advanced
Every proper Sudoku has exactly one solution, and you can always reach it by logic — no guessing required. Solving is about knowing where to look. These techniques are listed roughly in the order you'll need them, from easy puzzles to hard ones.
Scanning (cross-hatching)
Pick a digit — say 5 — and look at every 5 already on the board. Each one rules out its whole row and column. Now look at a box that doesn't have a 5 yet: if only one empty square in that box isn't ruled out, the 5 must go there.
Go through the digits from 1 to 9 like this, starting with the ones that appear most often. On easy puzzles, scanning alone solves most of the grid.
Naked singles
Look at one empty square and list what's already in its row, column and box. If eight different digits are used, the ninth is the only one that can go there.
Hidden singles
Sometimes a square could hold several digits, but one of those digits has nowhere else to go in its row, column or box. Then it must go in that square, even though other digits looked possible.
Pencil marks
On harder puzzles, write the possible digits (candidates) in each square. It's slower at first but makes the advanced techniques visible. Update the marks every time you place a digit — in our Sudoku, placing a digit clears it from the notes in its row, column and box automatically.
Naked pairs
If two squares in the same row, column or box can each only be the same two digits — say 3 and 7 — then those two squares will take the 3 and the 7 between them. That means 3 and 7 can be crossed off every other square in that row, column or box.
The same idea works with three squares and three digits (a naked triple).
Pointing pairs
If, inside one box, a digit can only go in squares that all lie in the same row, then the digit must be in that row within that box — so you can remove it from the rest of that row outside the box. The same works for columns.
The X-wing
For tough puzzles: suppose a digit can only go in two places in one row, and in exactly the same two columns in another row. Those four squares form a rectangle, and the digit will fill two opposite corners. Either way, it takes both columns — so it can be removed from every other square in those two columns.
Solving faster
- Don't stare at one spot when you're stuck — switch to a different digit or a different box.
- Finish easy placements first; each one makes the next easier.
- Check your work as you go. A single wrong digit can make a puzzle look impossible later.
- Practise daily. Speed comes from recognising patterns, and patterns come from repetition.