Competitive Programming Sites

Competitive Programming sites as far as I can find

- Codeforces (also has acmsguru)

- Atcoder (short problem statements) -- Problem difficulty: https://kenkoooo.com/atcoder/

- DMOJ (IOI and ICPC problems)

- Kattis (ICPC problems)

- Advent of Code 

- Timus

- Project Euler

- dunjudge.me

- UVa Online Judge/Online Judge

- Topcoder

- CodeChef

- oj.uz (IOI and ICPC)

- acmicpc.net (ICPC problems because Live Archive is slow)

- USACO

- Leetcode

- Hackerrank

- e-olymp (olympiad)

- toph.co

- acmp.ru (short problem statements)

- judtge.org 

- URI Online Judge (ICPC)

- SPOJ 

- SGU on Codeforces (harder problems) 

- PEG (migrated to DMOJ, was mostly OI problems) 

- CSES

- Aizu (has JOI) (https://onlinejudge.u-aizu.ac.jp/) -- JOI problems difficutly: https://joi.goodbaton.com/

Also another big list here: https://clist.by/resources/