Sudoku solving technique · Intermediate
Box/Line Reduction
If a digit in a line sits inside one box only, it leaves the rest of that box.
What is Box/Line Reduction?
The reverse of a Pointing Pair. When a candidate in a row or column only appears within a single block, it must go in that block. You can eliminate that candidate from all other cells in the block that are not in that row or column.
How to spot Box/Line Reduction
You look the other way round from a Pointing Pair. Go along a row or column and check whether all candidates of a digit lie in the same box. Then the digit must be on that line inside the box, and you can remove it from the other cells of the box.
- Difficulty
- In Sudoku Pro, this technique belongs to the Intermediate level.
- Learning path
- Technique 6 of 20 on the learning path
An example from the app
| Pattern (purple). Candidates 2, 3 | Pattern (purple). Candidates 2, 3 | Given 1 | Given 4 |
| Affected cell (orange). Candidates 1. Eliminated 3 | Given 4 | Given 2 | Empty |
| Empty | Given 1 | Empty | Empty |
| Given 4 | Empty | Empty | Empty |
Small digits are candidates. Crossed-out digits can be removed in this step.
- Pattern (purple)
- Affected cell (orange)