If you've never played Connect 4, you can play it for free at http://www.connectfour.org. It's a quick and fun game. Basically, two players take turns dropping different-colored discs into a grid of six rows by seven columns from the top of a column. The newly dropped disc either sits at the bottom of a column, if no discs have been dropped in that column, or on top of the last dropped disc in that column. Whoever first has four consecutive discs of their own color in any of the three possible directions (horizontally, vertically, diagonally) wins the game.
The AlphaZero model for Connect 4 was based on the https://github.com/jeffxtang/DeepReinforcementLearning repo, a fork of https://github.com/AppliedDataSciencePartners/DeepReinforcementLearning, with a nice blog on How to build your own AlphaZero AI using...