Bridges: bridges can’t cross
A bridge is a wall for every bridge that would cross it. Each one you draw takes neighbors away from the islands on either side, and the counting gets easier.
How it works
Two bridges never cross. That rule does more than stop you drawing over a line: it changes the count.
When an island counts its neighbors, a neighbor on the far side of a drawn bridge doesn’t count. It can take nothing from this island. So the most the island could get drops, and a number that had room to spare may now need every bridge it has left.
Look for long bridges
Long bridges block the most. After you draw one, check the islands on both sides of it. Each may have lost a neighbor, and an island that loses a neighbor often has its count settled.
Worth memorizing
A drawn bridge blocks every bridge across its path.
A blocked neighbor counts as zero.
Then count again.
Practice
0 of 2 rightCan the 3 in row 4, column 1 still send a bridge to the 2 on its right?
Where does the last bridge of the 3 in row 4, column 1 go?