Clone Sudoku: Rules and Solving Strategy

Map corresponding cells before solving

Clone Sudoku follows the classic rule that every row, column, and 3x3 box contains 1 through 9 once. It also marks two or more regions as clones. In the standard form, regions with the same color or outline contain identical digits in corresponding positions. If the top-left cell of one clone is 4, the top-left cell of its partner clone is also 4. The shapes usually have the same orientation, so you can pair their cells by translating one region to the other. Some custom puzzles allow rotation or reflection, but that must be stated explicitly. Do not invent a transformation from the picture. Draw or mentally label the matching positions before entering candidates. A clone region may be a straight line, a bent shape, a rectangle, or a scattered set defined by the puzzle. Shapedoku's normal boards do not include clone markings, but the principle fits symbol Sudoku naturally because corresponding clone cells would carry the same glowing shape.

Intersect the candidates of every clone pair

Corresponding clone cells are equal, so their candidate lists should always match the intersection of what both locations allow. Suppose one clone cell can contain 2, 5, or 8 from its row and box, while the corresponding cell can contain 1, 5, 7, or 8. Both cells are therefore limited to 5 or 8. Any candidate removed from one location must be removed from its partner. This transfer can cross the entire grid and connect units that otherwise have no direct relationship. A placement travels the same way: solving either cell solves both. Update all linked copies before continuing, especially when more than two regions share the same clone pattern. A candidate that survives locally may still fail globally because one corresponding location cannot support it. Full Notes make these intersections visible, but keep the mapping clear. Accidentally pairing the wrong positions can produce a beautifully consistent disaster, which is still a disaster despite the symmetry.

Use clone placements to create distant unit effects

Clone equality becomes strongest when corresponding cells occupy different kinds of units. A value ruled out by a column on one side may disappear from a box on the other side, creating a hidden single there. If two corresponding clone cells happen to share a row, column, or box, equality would normally force an illegal repeated digit, so valid puzzle construction usually avoids such a mapping unless another rule changes the interpretation. Clone regions can also create subsets. If three positions in a clone shape are collectively restricted to 2, 6, and 9, the corresponding three positions in every copy use the same ordered values. Solving the order in one region immediately resolves it everywhere. Work from the most constrained copy, not necessarily the first one drawn. After each candidate intersection, inspect every row, column, and box touched by all copies. The extra rule does not replace classic Sudoku logic. It acts as a bridge that carries ordinary deductions from one location to another until one side becomes more informative than the other.

1. Identify every clone region and confirm its orientation from the puzzle rules.
2. Pair corresponding cells and label their positions consistently.
3. Replace each pair's candidates with the intersection allowed at both locations.
4. Copy every placement and elimination to all matching cells.
5. Inspect every affected row, column, and box after information transfers.
6. Use the most constrained clone copy to guide the others rather than solving regions separately.