It's that when I looked at this code: https://mirror.codeforces.com/contest/2231/submission/375517331.

I tried to maximize the run-time on this code on my PC, but it took at most 800ms, even if I generated very similar tests as test 20 for example. (I'm trying to maximize mp's size, which is over $$$2.3\times 10^6$$$ in my tests, while test 20 is only $$$2.2\times 10^6$$$. I've also considered umap killer tests, and they peaked at about 1.5s on my system.)

This is probably a compiler/OS difference on Codeforces.

I'm using a 3.6 GHz Core i7-10750H (the extra L3 cache doesn't have much effect) and GCC 16.1.1 on Linux... Codeforces is using the same 3.6 GHz Skylake core with less L3 cache. Could anyone reproduce this?