We ended up making a meme contest, here’s the announcement for the contest; the original announcement is here. Hi Codeforces! We are pleased to invite you to [contest:383377], which will take place on [contest_time:383377]. You will be given 9 problems and 2 hours to solve them. Please follow this link in order to register for the contest. Note that this contest is not an official Codeforces round. The round will be unrated for all participants....

This post was originally written on Codeforces; relevant discussion can be found here. This post will be more about developing ideas about certain structures rather than actually coding up stuff. The ideas we’ll be developing here have many applications, some of which involve: Number Theoretic Möbius Inversion Principle of Inclusion-Exclusion Directed Acylic Graphs Subset Sum Convolution Finite Difference Calculus (and prefix sums) Note that some of the terminology used below might be non-standard....

This post was originally written on Codeforces; relevant discussion can be found here. As a certain legendary grandmaster once said (paraphrased), if you know obscure techniques and are not red yet, go and learn binary search. The main aim of this tutorial is to collect and explain some ideas that are related to binary search, and collect some great tutorials/blogs/comments that explain related things. I haven’t found a comprehensive tutorial for binary search that also explains some intuition about how to get your own implementation right with invariants, as well as some language features for binary search, so I felt like I should write something that covers most of what I know about binary search....

This post was originally written on Codeforces; relevant discussion can be found here. Introduction A while ago ToxicPie9 and I made and posted this meme: To my surprise, many people are quite confused about it. In fact, I realized there are a lot of misconceptions about pragmas. Most C++ users on Codeforces put a few lines of pragmas at the start of every submission. However, I believe many of them don’t fully understand what they’re doing or how pragmas work; the only thing people seem to think is that “add pragmas -> code go brr”....

This post was originally written on Codeforces; relevant discussion can be found here. In this post, I will focus on the following problem: 920E. More generally, we will look at how to do efficiently traverse the complement graph of a given graph in both dfs and bfs orders. In particular, the bfs order also allows us to find a shortest-path tree of the complement graph. This is my first post, so please let me know of any errors/typos that might have crept in....