How to optimally solve the flood fill puzzle?

Question

I like playing the puzzle game Flood-It, which can be played online at:

https://www.lemoda.net/javascript/flood-it/game.html

It\'s also available as an iGoog

Answer 1

Here's an idea for implementing the graph to support Smashery's heuristic.

Represent each group of contiguous, same-colour squares in a disjoint set, and a list of adjacent groups of squares. A flood fill merges a set to all its adjacent sets, and merges the adjacency lists. This implicit graph structure will let you find the distance from the upper left corner to the farthest node.