Connect the islands with bridges. The number on an island is exactly how many bridge ends must touch it.

• Bridges run straight across or down — never diagonally, never crossing another bridge.
• At most two bridges join the same pair of islands.
• Tap one island then another to add a bridge; tap the pair again for a double, again to remove.
• When you are done, every island must be reachable from every other — one network.

A 1 next to a 1 can never be joined (that would strand them), and an island marked 4 in a corner has both its bridges doubled — those are the openings.