Bridges #521 · 9×9

• 9×9grid
• 14islands
• 17bridges
• 4double routes

Bridges #521 is a 9×9 grid at medium level with 14 islands. The solution lays 17 bridges along 13 routes, and 4 of those routes carry a double bridge. The largest number on the map is 4.

You can start without any guessing: 3 islands have a number equal to or one below twice the neighbours they can see, so every one of those neighbours gets at least one bridge.

2 islands carry a 1. Two of them may never be linked to each other, because that pair would be cut off from the rest of the map.

One island sits in a corner of the grid, where it can see at most two neighbours: a good second place to look.

Medium grids also need the isolation rule: rule out any bridge that would close a group of islands off from the rest of the map.