Bridgework

About this game

Bridgework is the puzzle usually called Bridges, or Hashiwokakero. A scatter of islands sits on a grid, each stamped with a number, and you join them with bridges running straight along the rows and columns. An island takes exactly as many bridge ends as its number says, no pair may be joined by more than two, bridges never cross, and when you are finished every island has to belong to one single network rather than a few tidy islands of its own. That last condition is the one that catches people, and on the larger boards it is the difference between a board that looks finished and one that is. What separates this from most versions is what happens before you see a board. Each one is dealt, then checked twice: once to prove that exactly one arrangement of bridges satisfies it, and again to prove that a solver using only human techniques can actually reach that arrangement. Boards failing either test are thrown away and never shipped. So the promise is a strict one — you will never need to guess, and you will never reach the end and find two possibilities left. The difficulty labels mean something specific too. Easy and Medium boards are settled entirely by counting: work out what an island's number allows and the bridges follow. Hard and Expert boards additionally require you to assume something, follow it until it breaks, and rule it out — the same reasoning, one step deeper. Grids run from seven squares across up to fifteen, and forty-odd islands. A hint will look at the board as you have actually left it and tell you the next thing that is forced and why it is forced, rather than simply pointing at a square; and if you have built something that cannot be right, it says that instead. A new crossing arrives every day, gentle at the start of the week and expert on Sunday, with a streak to keep and hint-free solves counted separately.

Controls

Drag from one island to another to build a bridge, or tap the two islands in turn. Repeating it adds a second bridge, and once more clears them.

Keyboard

• Arrow keys build from the selected island.
• Shift and an arrow moves the selection instead, Tab cycles islands.
• Z undoes, H asks for a hint, R resets.

How to play

Each island must end with exactly as many bridge ends as the number it carries.

Building

• Bridges run only straight up, down, left or right, only between two islands that can see each other along that line, and never through a third island.
• Two islands may be joined by one bridge or two, never more.
• No bridge may cross another.
• Finally — and this is the condition people forget — every island must end up joined into one single network, so a group that satisfies all its own numbers but sits apart from the rest is not a finished board.

On the board

• Drag between two islands to build, drag again for a second bridge, once more to clear.
• Islands turn gold when their number is met and red if you overshoot.
• Undo and reset are free, and a hint will tell you the next forced bridge and the reason it is forced.

Read the full Bridgework rules and strategy →