Clone Sudoku
Marked regions must contain identical digit arrangements
What is Clone Sudoku?
Clone Sudoku marks pairs of regions (clones) on the grid. Each pair of clone regions must contain exactly the same arrangement of digits — if one clone has a 3 in its top-left cell, the other clone must also have a 3 in its corresponding cell. Clone constraints create powerful symmetry-based deductions that can resolve entire regions at once.
At a Glance
| Constraint type | Clone Regions |
| Typical givens | 24–32 |
| Difficulty rating | ★★★★☆ 4/5 |
| Avg. solve time — Easy | 10 min |
| Avg. solve time — Medium | 22 min |
| Avg. solve time — Hard | 42 min |
| Avg. solve time — Expert | 72 min |
How to Solve Clone Sudoku
| Technique | What it does | Level |
|---|---|---|
| Clone Pair Deduction | Any digit placed in one clone region immediately forces the same digit in the corresponding cell of the other clone region. | Beginner |
| Constraint Propagation | A clone placement propagates through standard row, column, and box constraints in both regions simultaneously. | Intermediate |
| Clone-Box Interaction | If both clone regions share boxes with heavily constrained cells, the clone constraint rapidly resolves entire boxes. | Intermediate |
| Mirror Elimination | When a digit is eliminated from a position in one clone region by standard logic, it can be eliminated from the same position in the other clone region. | Advanced |
| Multi-Clone Logic | With two clone regions, solving either provides equal information about both. Alternate deduction paths between clones for maximum efficiency. | Advanced |
Average Solve Times
Easy
10 min
Medium
22 min
Hard
42 min
Expert
72 min
Frequently Asked Questions
Must clone regions contain the same digits in the same order?
Yes — corresponding cells (same position within the region shape) must hold the same digit.
Are clone regions always the same shape?
Yes — clone regions in a puzzle are always identical shapes, just placed in different locations.