Plumbing

Goal

The pipe network has been taken apart: every tile has been rotated at random. Turn them so that all tiles are connected to the central source, with no open ends. As soon as a pipe is connected, water rushes into it; when the network is complete, it reaches the last basin.

Controls

• Tap or click: rotate a quarter turn clockwise.
• Right-click or Shift + click: rotate the other way.
• Long press or middle-click: lock a tile you are sure about; it no longer rotates until you unlock it.
• Keyboard: arrow keys to choose a tile, Space to rotate, Backspace for the reverse direction, L to lock.

Wrapped edges

At the Expert and Diabolical levels (or if you turn it on in the options), the board wraps around on itself: a pipe that leaves through the right comes back in on the left, and a pipe that leaves through the top comes back in at the bottom. The margins of the board show the tiles from the opposite side in transparency.

About the generator and the solver

Each network is a random spanning tree built by biased growth (with no four-way crosses), then every tile is rotated at random: a solution always exists. The hint queries a solver (arc consistency, elimination of loops and closed networks, then depth-first search) and fixes first a tile whose orientation can be deduced logically, close to the part that is already supplied.