Hard Clone Sudoku

Shaded regions are clones — identical in digit content and position. One placement updates all its clones simultaneously.

Easy Medium Hard Expert

Hard Clone Sudoku. Fewer givens and complex clone-region interactions — expect multi-step bi-directional propagation and extensive pencil-mark tracking.

8
6
3
9
5
2
3
9
4
6
1
3
5
9
4
2
5
4
3
9
2
1
8
6
1
8
3
Clone A Clone B Both regions must have identical digits
Mistakes
0/3
Score
-
Time
00:00
Try Expert Clone Sudoku →
Progress0%

What is Clone Sudoku?

Difficulty
★★★★☆
4/5
Constraint Type
Clone Regions
Typical Givens
24–32
Avg. Solve (Hard)
42 min

Solving Techniques for Hard Level

Technique Description 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

Ready for the ultimate test? Try Expert Clone Sudoku — the hardest puzzles on Sudoku.by.

Techniques to Master at Hard

  • Hidden Pairs technique — Twin-imported eliminations thin cells invisibly — recount the boxes hosting each clone region after every mirror update, because that's where hard clone grids hide pairs.
  • X-Wing technique — Eliminations exported through the clone link land in rows the original logic never touched — re-scan for X-Wings after each mirror transfer, not just after direct placements.

Average Solve Time by Difficulty

Easy
10 min
Medium
22 min
Hard
42 min
Expert
72 min
Want a full walkthrough of rules, strategies, and solving steps? How to Play Clone Sudoku →

Related Variants

Chaos Construction

Structure-as-puzzle taken to the limit: instead of mirroring known regions, you deduce where the regions even are.

Jigsaw Sudoku

Region-shape reading without the mirroring — nine snaking regions replace the standard boxes.

Diagonal Sudoku

Like clone cells, diagonal cells link distant parts of the grid — placements echo far beyond their own box.

Frequently Asked Questions — Hard Clone Sudoku

What makes hard Clone Sudoku difficult?
Hard puzzles have fewer given digits and clone regions that intersect with each other's rows, columns, or boxes in complex ways. You need to track bi-directional clone propagation and standard advanced techniques like naked pairs, hidden pairs, and pointing pairs simultaneously.
How do I use the clone constraint for advanced eliminations in hard puzzles?
Look for a cell in Clone A where only two digits remain. Both those digits must also be candidates in the corresponding Clone B cell. If the Clone B position is in a row/column that already eliminates one of those digits, you've solved both cells simultaneously.
Should I use pencil marks for hard Clone Sudoku?
Absolutely. Hard Clone Sudoku requires tracking candidates across both clone regions plus all rows, columns, and boxes. Without pencil marks, the cross-clone interactions become impossible to follow reliably.
What is the hardest type of deduction in hard Clone Sudoku?
The trickiest deductions involve a digit that is forced into one cell of Clone A purely through clone logic (the corresponding Clone B cell is confined by external row/column constraints), which then unlocks a cascade through both clones and several boxes.
How long does a hard Clone Sudoku take?
Expect 20–40 minutes. The harder the puzzle, the more important it is to set up your pencil marks systematically across both clone regions before attempting any speculative placements.

More questions? See the full Clone Sudoku guide.