Coding Challenge idea: Circle the Cat

There's a great old turn-based Flash game called Circle the Cat.

https://www.google.co.uk/search?q=circle+the+cat

The Cat starts in the middle of a hexagonal grid and you have to build a wall of circles to stop it from escaping. Each game starts with randomly pre-placed circles and the game ends either when the cat escapes off the edge or you have managed to successfully trap it.