Flood-It

How to play

Your flood starts at the top-left corner. Pick a color and the flood turns that color, swallowing every touching square that already matches. Fill the whole board with one color in 25 moves or fewer.

Harder than it looks

Finding the fewest possible moves for a Flood-It board is NP-hard, the same family of problems as the traveling salesman. Nobody knows a fast way to find the perfect solution, so every good move you make is a guess backed by intuition.