I have always been curious about my ranking in the leaderboard as a function of time, since I have always suspected that I am rather slow on easy problems.

To learn Angular, I built a web app that displays your ranking throughout any given contest.

If you are interested, please give it a try: https://megaspazz.github.io/CodeRank/

As of now, it works with normal CF rounds and ICPC-style rounds; it should probably work with IOI-style contests, but they seem to be rare on Codeforces. It doesn't really work for marathon-style contests.

Example screenshot:

Some notes:

1. Codeforces API sometimes doesn't report hacks for contests, for example API link for Codeforces Round 576 (Div. 1) seems to always report an internal error.
2. It's hosted serverless on Github pages, so I manually pre-process all of the contests so that the JSON only contains data the app needs and it avoids hitting the Codeforces when people use the app.

I saw in the comments of Codeforces Round #823 (Div. 2) that many C++ users needed to use setprecision to get AC on problem B. Fortunately, as a Java user, I didn't face the issue this time, but it made me wonder: what are some "gotchas" that people who are newer to competitive programming should look out for?

I also recall that in last year's FB HackerCup, where we need to run code locally, a friend of mine who uses C++ didn't set their local stack size high enough and therefore couldn't successfully run their otherwise-correct code on the full input set.

I know for Java, I painfully learned early on that Java's sort routines on primitive arrays have worst case O(n^2) runtime using a Quickselect variant, and that very smart hackers can construct adversarial inputs that cause a Java solution to get TLE.

So, in your experience, what are some things that have tripped you up?