When a row claims a region
Suppose row 4 still needs a crown and every legal cell on that row belongs to region C. Row 4 must receive C's crown. C therefore cannot place another crown on any other row, so its candidates outside row 4 are excluded.
This is the reverse of a region claiming a row. Check the direction before marking: region-to-line removes other regions on the line; line-to-region removes the same region away from the line.
- Find a row or column whose remaining candidates all have one region letter.
- Eliminate that region's candidates outside the claimed line.
- Several cells on the line may remain. The rule reserves the region; it does not automatically pick a cell.
Why it works
If every legal cell in a row belongs to the same region, that row's crown must come from that region. The region can only have one crown, so it cannot place it anywhere else: all of its cells outside the row are eliminated. It is the mirror image of a region claiming a row.
How to spot it fast
- Scan rows and columns that are almost full of eliminations: the few cells left often share one color.
- Check lines that cut through the middle of a large region; edge lines are frequently claimed by one big region.
- After applying it, rescan the claimed region — removing its outside cells often frees other regions.
Common mistakes
- Mixing up the direction. Line-claims-region removes the same region elsewhere; region-claims-line removes other regions on the line.
- Calling it with one stray cell of another color still on the line. The rule needs every legal cell on the line to share the region.
Try one move
Tap a still-open cell this deduction rules out. This is a real position from 5×5 puzzle #5-standard-001.
👑 placed crown · × already ruled out · · still a candidate. Row and column numbers start at 1.
A real example from the game
This position comes from 7×7 puzzle #4, after 4 earlier deductions. The highlighted cells show where the technique applies.
A row claims a region
Row 1 can only receive its crown from region A, so that region must spend its crown here — its cells on other rows are ruled out.
Play this board and look for the same move yourself.
How often this technique appears
Across all 4,000 levels, our logic engine needs this technique on the following share of boards at each size:
| Board size | Boards that need it |
|---|---|
| 5×5 | 34% |
| 6×6 | 33% |
| 7×7 | 37% |
| 8×8 | 49% |
| 9×9 | 46% |
| 10×10 | 78% |
| 11×11 | 64% |
| 12×12 | 66% |
Questions about this technique
What is the difference between a region claiming a row and a row claiming a region?
A region claims a row when all its cells lie in that row (eliminate other regions on the row). A row claims a region when all the row's cells belong to one region (eliminate that region's cells off the row).