Some notes for cp training.

E689120's "A way to pratice competitive programming":
https://codeforces.com/blog/entry/66909;
https://drive.google.com/file/d/1J2x8pIYQ3MXANgvzOgBciWd3d79j_Exa/view

A list of competitive programming related things:

• https://codeforces.com/
• https://atcoder.jp/
• https://vjudge.net/
• http://usaco.org/
• http://hsin.hr/coci/
• https://szkopul.edu.pl/
• http://orac.amt.edu.au/cgi-bin/train/hub.pl
• https://dmoj.ca/
• http://acm.timus.ru/
• https://www.acmicpc.net/
• https://www.ioi-jp.org/
• https://csacademy.com/
• https://www.spoj.com/
• https://oj.uz/
• https://open.kattis.com/
• https://wcipeg.com/main
• http://judge.u-aizu.ac.jp/onlinejudge/
• http://noi.ac/
• http://uoj.ac/
• https://www.hackerrank.com/
• https://www.codechef.com/
• http://ceoi.inf.elte.hu/
• Baltic Olympiad in Informatics
• Balkan Olympiad in Informatics

Learning sites:

• http://cp-algorithms.com/

Blogs:

• https://codeforces.com/blog/entry/60442 Rolling hash
• https://codeforces.com/blog/entry/57282 List of cp tutorials
• https://codeforces.com/blog/entry/48417 General tricks
• https://codeforces.com/blog/entry/70178 On problem setting
• https://codeforces.com/blog/entry/70740 Min-cost max-flow complexity
• https://codeforces.com/blog/entry/62359 "Looking for a challenge" problems
• https://codeforces.com/blog/entry/52341 References for "the largest-area inscribed triangle in a convex polygon" algorithm
• https://codeforces.com/blog/entry/15547 Catching silly mistakes with GCC
• https://codeforces.com/blog/entry/69186 Codeforces's gym contests with editorials

Math sites:

• https://projecteuler.net/

Random sites:

• http://mxwell.github.io/draw-graph/ (csacademy.com also has a similar application but with interaction)

Communities:

• https://codeforces.com/blog/entry/52778 Biggest Discord server