Does it play Connect Four? Yes, it does.

Based on how well my Monte Carlo Tree Search agent played Tic Tac Toe, I wanted to move onto Connect Four.

Because the algorithm is domain independent I merely had to add the logic to list valid moves and determine a win, loss or draw outcome. One half-hour commute later and I had it playing Connect Four!

And it plays well, in fact really really well. Despite me trying my very best and with help from my wife, who happens to beat most of our family and friends at this game, we cannot beat the AI, when it plays first. Connect Four has been fully solved by MinMax searches and it can be shown that the first player can always force a move. This is exactly what my MCTS agent does. It will setup various potential win cases at the higher level slots and then eventually force you into playing moves that will allow it to win.


The other nice thing about the playing style you get from MCTS is that even if you play the same moves against it, due to its random sampling of the search tree, it will typically come up with slightly varied responses - ultimately leading to a win of course! :)

What's next? I'm currently deciding on whether to move onto 9x9 Go, some other intermediate step, or perhaps spend a bit of time making simple web-based GUIs for the Tic Tac Toe and Connect 4 agents, as my current UI is a bit lacking...see insert :)