Chokepoint
Hard
Used by Smart Hint
If the only way to reach a cell is through one narrow gap, and going that way traps a 2×2 sea block, the gap must be land.
- Sea
- Cells that establish the pattern
How it works
- Picture a cell where the only route past it leads straight into what would become an illegal 2×2 sea block one step later.
- Rather than waiting for that block to actually form (the plain No 2×2 Sea rule), this checks one step ahead: if sending this cell to sea would immediately force a neighbor into an impossible spot — touching two islands at once, or reachable by no island at all — the sea move was never legal to begin with. The cell is land.
- Applied at the board's edge instead of an interior corner, this is also what "Edge and Corner Turning Rules" describes: a sea path meeting the boundary needs the same one-step-ahead check to avoid trapping itself.