Overlap Scanning: Step-by-Step Guide
When a clue is long, counting from the left and from the right forces certain tiles to overlap. Those shared cells are guaranteed fills even before the full run is placed.
Prerequisites
How to recognize it
- Take a long clue and slide it from the left edge, marking the cells it could cover.
- Repeat from the right edge; any tiles highlighted by both passes must be filled.
- Use the overlaps to place confident X marks on the cells outside the shared region.
Why it works
Every placement of a run must span the same number of cells. Overlap scanning captures the intersection of all legal placements, revealing squares that stay filled across every scenario.
Try it now
Interactive example coming soon: drag markers from each side of a clue to see overlapping tiles appear.
Common pitfalls
- Overlooking mandatory one-cell gaps between different clues when sliding from each side.
- Forgetting to revisit the line after new fills—fresh overlaps often appear.
Related: Confident Marking