Technique Guide
Sudoku solving techniques
Twenty techniques that solve a Sudoku without guessing. They appear in the order Sudoku Pro introduces them on its learning path, from the singles for beginners to the XY-Chain for experts. Each page explains one technique with an example board from the app.
Beginner
- Naked Single
A cell where only one digit can still go.
- Hidden Single
A digit that has only one place left in a row, column or block.
Intermediate
- Naked Pair
Two cells with the same two candidates lock those digits for their unit.
- Hidden Pair
Two digits that appear in only the same two cells of a unit.
- Pointing Pair
If a digit in a box sits on one line only, it leaves that line outside the box.
- Box/Line Reduction
If a digit in a line sits inside one box only, it leaves the rest of that box.
- Naked Triple
Three cells whose candidates add up to only three digits.
- Hidden Triple
Three digits that appear in only the same three cells of a unit.
- X-Wing
A digit locked to the same two columns in two rows leaves the rest of those columns.
Pro
- Skyscraper
An almost X-Wing: two base cells share a column, the two roofs do not.
- Swordfish
The X-Wing across three rows and three columns.
- 2-String Kite
A row and a column with two candidates each, joined through a box.
- W-Wing
Two matching two-candidate cells, joined by a digit that appears only twice in a unit.
- Y-Wing
Three cells with two candidates each: a hinge and two wings.
- XYZ-Wing
Like a Y-Wing, but the hinge has three candidates.
Expert
- Unique Rectangle
A rectangle of four cells that would otherwise allow two solutions.
- Finned X-Wing
An X-Wing with extra cells, the fins, inside one box.
- Simple Coloring
Following one digit through strong links in two colors.
- Jellyfish
The X-Wing across four rows and four columns.
- XY-Chain
A chain of two-candidate cells whose ends share a digit.