https://www.codingame.com/ regularly holds 10-day long competitions where you should write a program that plays a 2-player game. Sometimes you must move units/soldiers in a grid, sometimes it's a card game. The next game starts tomorrow (Friday) and then we'll see what's the topic (well, it must be food related).
No prerequisites needed. I will explain my thoughts and give general advice for this type of contests. Feel free to ask questions in chat.