Clone Sudoku
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Clone A
Clone B
Both regions must have identical digits
How to play Clone Sudoku
Standard Sudoku rules apply. Two highlighted regions (Clone A in amber, Clone B in purple) must contain identical digit arrangements — corresponding cells must hold the same digit. Placing a digit in one clone automatically constrains the same position in the other clone.
Full guide →
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
What is Clone Sudoku?
Clone Sudoku is a variant where two highlighted regions of the same shape appear on the grid. The two regions are 'clones' — they must contain exactly the same digit arrangement. Every cell in one region holds the same digit as the corresponding cell in the other region. Standard Sudoku rules apply.
How do the clone regions correspond?
The two clone regions are the same shape and size. Each cell in one region is paired with the corresponding positionally-equivalent cell in the other region. Placing a digit in any cell of one clone immediately fixes that digit in the matching cell of the other clone.
Can clone regions overlap with the same rows or columns?
Yes. The puzzle constructor ensures that the clone constraint is always consistent with Sudoku rules — the two regions are positioned so that corresponding cells are in different rows, columns, and boxes, allowing the same digit to appear in both without violating uniqueness.
Is Clone Sudoku harder than regular Sudoku?
The clone constraint effectively halves the number of independent cells to solve — every deduction in one region automatically applies to the other. Easy Clone puzzles resolve noticeably faster than classic Sudoku. Hard and expert puzzles use the clones to create complex bi-directional constraint chains.
What is the best strategy for Clone Sudoku?
Treat the two clone regions as a single constraint. Whenever you eliminate a candidate from a cell in one region, immediately eliminate it from the corresponding cell in the other. Focus on the rows, columns, and boxes that interact with both regions simultaneously.
How long does Clone Sudoku take to solve?
Easy puzzles take 6–15 minutes. Medium puzzles run 15–30 minutes. Hard puzzles average 30–60 minutes and expert puzzles can take 60–90 minutes. The bilateral nature of the clone constraint makes mid-game breakthroughs especially satisfying.