Plankway

Avoid isolation: never close off a finished group

The last rule, one connected network, is the one beginners forget and experienced players use the most. A bridge that would finish a group of islands while other islands are still outside it can never be right.

Two 1s never connect

If two islands with a 1 were connected, both would be full, and together they would form a tiny network of two with no way out. Unless those are the only two islands on the board, that is impossible.

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A bridge between the 1 in A1 and the 1 in D1 would close them off. It is ruled out.

Here that settles the whole puzzle: each 1 must connect downwards instead, and the two 2s connect to each other.

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The solution: one network of four islands.

Two 2s never take a double bridge

The same logic for two 2s: a double bridge between them fills both up and closes them off. One bridge between them is fine, two is not.

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A double bridge between the two 2s would isolate them, so there is at most one.

Bigger groups

The real power of this technique shows on bigger boards. Late in a puzzle you will often have a group of several islands that is nearly complete. Before you add the last bridge inside that group, ask: would this finish the group while it is still cut off from the rest? If so, the bridge must go elsewhere, usually outwards.

Plankway helps you see this: a finished group that is cut off gets orange flags. In the solver, isolation has weight 3 out of 6, and it is the technique that separates Wednesday from Monday. The next step up is the only way out, which looks at the same network rule from the other side.

Recent puzzles that needed this technique

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