Box Brain Sudoku
Sudoku techniques, step by step
The eighteen techniques the app teaches, in the order it teaches them. Each one has a worked example from a real puzzle. Every puzzle in Box Brain Sudoku can be solved with these alone, no guessing.
Easy
- 1
Naked Single
A cell has only one candidate left.
- 2
Hidden Single
A digit has only one place left in a row, column or box.
- 3
Thermometer Bounds
Digits rise along a thermometer, starting at the bulb.
- 4
Cage Combinations
Only some sets of digits add up to a cage's total.
- 5
Arrow Sums
The digits on an arrow add up to its circle.
- 6
Kropki Dots
Dots fix how neighbouring digits relate.
- 7
Greater Than Signs
A sign tells you which of two neighbours is bigger.
- 8
Sandwich Sums
A sandwich sum limits where the 1 and the 9 can go.
Medium
- 9
Naked Pair
Two cells in a house share the same two candidates, and nothing else.
- 10
Hidden Pair
Two digits can only go in the same two cells of a house.
- 11
Pointing Pairs
Within a box, a digit fits only along one row or column (or the other way round).
- 12
The 45 Rule
Every row, column and box adds up to 45.
Hard
- 13
Naked Triple
Three cells in a house hold only three digits between them.
- 14
Hidden Triple
Three digits can only go in the same three cells of a house.
- 15
X-Wing
In two rows, a digit fits in exactly two cells, and those cells line up in the same two columns.
- 16
XY-Wing
A pivot with candidates XY sees two pincers, XZ and YZ.