Fall 25 - Week 1

Welcome to the first week of competitive programming of the Fall of 2025! If this is your first time attending a session please read the following carefully, otherwise feel free to proceed to the usual problem-solving.

If this is your first time ever doing competitive programming of any kind, please complete our new introduction guide to get started.

Each of our sessions consists solving a few coding algorithmic problems. You are free to do so however you’d like. You can collaborate with other people, you can ask for help, etc. You can also use AI if you’d like, but I’d recommend restricting the AI use, otherwise it defeats the purpose of learning. My personal suggestion is to limit AI use to the Copilot autocomplete coding features. Avoid asking AI for solutions. (Note that if you decide to compete on official competitive programming events, you won’t be able to use any AI. So if you want to practice for competitions, don’t use any AI).

Our sessions have two sets of problems, intended for different audiences.

• Learn Division. If you have no experience with competitive programming, or you are not very comfortable designing and coding algorithms, this is the right level for you. We provide a guide with each problem set, containing some optional background reading, and then some hints/advice per problem. The level of the problems ranges from an easy COS126 problem to a hard COS226 problem.
• Compete Division. If you want something beyond the above, this is the right division for you. The provided problems won’t have any background reading material or hints/advice, so it’s a more open-ended problem-solving environment. The first two problems of each session should be approachable if you are comfortable with COS226 level problems. Don’t assume the first problem is always the easiest, always look at the first two problems. The Compete Division problem set will be on contest mode on Codeforces, so there will be an informal, ranked scoreboard every week. You can always solve the problems after the session is over.

If you are not sure which of the above is the right fit, try one and then switch if you don’t feel comfortable.

Here is a list of things you should do before getting started, if you haven’t done it already:

• Create an account on Codeforces and log in. This is the platform we use to host problems and submit solutions.
• Join our Codeforces group by going to the following link: https://codeforces.com/group/hNnRWqFua0/ and clicking on join on the right.
• Make sure you are on our Discord. We will post weekly updates and other information there. You can also use it to ask for help outside our sessions. Ask Pedro for an invite to get in.

You will find all the problems on the Codeforces group link above (you can also see the problems of all past sessions). The guides with problem information for the Learn division will be available in the Fall 25 page.

Here are the links to this week’s problem sets:

• Learn Division
• Compete Division

Happy solving!