I wrote a free puzzle game for Android phones, called Super Blox. The aim of each level is to change the colour of all blue blocks (squares) to green using the following rules:
- You can move any block or the red ball to an adjacent empty location (horizontally or vertically, but not diagonally).
- Once the red ball touches any blue blocks it instantly turns them green. This can happen to multiple blocks in one move.
- The blocks and the ball cannot leave the boundary of the level (black rectangle).
Here is the first challenging level from the game. Can you solve it in 21 moves?