An example Clone puzzle: the two shaded clones hold the same digits in the same arrangement - 3, 8 copied cell for cell.
Clone Sudoku shades two or more regions that are clones of each other: identical in shape, and filled with the same digits in the same arrangement. Whatever goes in one clone must be copied, cell for cell, into every other clone - a mirror that links distant parts of the grid together.
The rule: clones hold matching digits
Cloned regions share their shape wherever they sit, and corresponding cells hold the same value. Below, two three-cell clones both read 4, 7, 2 - the second is an exact copy of the first.
Two clones, both 4-7-2: corresponding cells always match.
A worked example, step by step
Suppose one clone is already filled with 4, 7, 2, and its twin is still empty.
Step 0. One clone reads 4-7-2; its twin is empty.
Step 1 - copy across. Corresponding cells must match, so the twin takes the same digits in the same order: 4, 7, 2.
Step 1. The twin is copied cell for cell: 4-7-2.
Step 2 - the copies feed the grid. Those newly-placed digits are ordinary values now: the copied 4, 7 and 2 clear their own rows, columns and boxes, often unlocking cells far from either clone. That reach - solving one clone helps the region around the other - is what makes Clone Sudoku tick.
Solving strategy
- Solve one clone, get the rest free. Every digit placed in one clone copies straight into its twins.
- Work both ends. A digit forced in either clone (by its own row, column or box) transfers to all the others.
- Mind the overlaps. If a clone and its copy share a row, column or box, the matching digits can't clash - a strong extra constraint.
- Feed the grid. Copied digits behave like givens for their rows, columns and boxes.
Common mistakes
- Copying in the wrong orientation. Clones match cell-for-cell in the same arrangement - line up the shapes carefully.
- Allowing a clash. If two clones share a unit, their matching digits must not break the no-repeat rule.
- Forgetting to transfer. Any digit placed in one clone must appear in all of them immediately.
- Ignoring ordinary Sudoku. Clone cells still obey their rows, columns and boxes.
Can I play it here?
Not yet - Clone Sudoku isn't one of the puzzle types SudokuStreak generates for now. But you can learn its rules above, and there's plenty here to sink your teeth into meanwhile:
- Browse all the Sudoku variants we do offer.
- Or print free puzzles from the printable PDF page.
Where to play it
Clone Sudoku belongs to the constraint family and runs on 9×9. It is not one SudokuStreak generates yet - but the deduction it trains is the deduction every Sudoku runs on.
Difficulty and type are two separate dials here: the type sets the extra rule, the level sets how much of the grid you start with. Expert Sudoku leaves 25 of the 81 cells filled, where the beginner tools dry up almost entirely; Evil Sudoku leaves 23, with no easy moves at all. Take it at the gentler end while the pattern is still new, and move up once it stops being a fight.