Sudoku solving technique · Expert
Unique Rectangle
A rectangle of four cells that would otherwise allow two solutions.
What is a Unique Rectangle?
A Unique Rectangle uses four cells in two rows and two columns that lie in exactly two blocks. Three corners hold exactly the same two candidates, and the fourth holds both of them plus others. If the fourth corner were also reduced to that pair, the two candidates could be swapped around the rectangle and the puzzle would have two solutions. So the fourth corner loses both candidates of the pair.
How to spot a Unique Rectangle
Look for four cells that form a rectangle across two rows and two columns and lie in exactly two boxes. If three corners hold only the same pair of candidates and the fourth holds that pair plus others, remove the pair from the fourth corner. The technique relies on the puzzle having exactly one solution.
- Difficulty
- In Sudoku Pro, this technique belongs to the Expert level.
- Learning path
- Technique 16 of 20 on the learning path
An example from the app
| Pattern (purple). Candidates 2, 4 | Given 3 | Pattern (purple). Candidates 2, 4 | Given 1 |
| Affected cell (orange). Candidates 1. Eliminated 2, 4 | Empty | Pattern (purple). Candidates 2, 4 | Given 3 |
| Empty | Empty | Empty | Given 4 |
| Empty | Empty | Empty | Given 2 |
Small digits are candidates. Crossed-out digits can be removed in this step.
- Pattern (purple)
- Affected cell (orange)