Unique Rectangle
advancedAvoiding patterns that would create multiple solutions
Unique Rectangle techniques rely on the assumption that the puzzle has only one solution.
Understanding the Concept
If four cells forming a rectangle contain only two candidates, the puzzle would have multiple solutions.
To maintain uniqueness, at least one corner must contain additional candidates.
Several types exist based on the pattern of extra candidates.
Type 1: One corner has extra candidates - remove the pair candidates from it.
Type 2: Two corners in same house have same extra - that extra must be placed.
Based on the uniqueness constraint, not pure logic.
Only works if puzzle is guaranteed to have unique solution.
Examples
UR Type 1
Rectangle with {1,2} in three corners, fourth has {1,2,5}. Remove 1 and 2 from fourth corner.
Pro Tips
- •Look for potential rectangles with two candidates
- •Check corners for extra candidates
- •Only use if puzzle source guarantees uniqueness
- •Different types require different eliminations
