HKOI and External Competitions
- HKOI Facebook Page: https://www.facebook.com/hkoi.org
- HKOI Online Judge: https://judge.hkoi.org
- International Olympiad in Informatics (IOI): https://www.ioinformatics.org/
- National Olympiad in Informatics (NOI): http://www.noi.cn
- International Olympiad of Metropolises (IOM): http://megapolis.educom.ru/en
- Programming competitions of other countries: http://olympiads.win.tue.nl/ioi/noi/
Programming Tools and References
- Orwell Dev-C++: https://orwelldevcpp.blogspot.hk/
- Code::Blocks: http://www.codeblocks.org/
- C++ Resources: https://www.cplusplus.com/
- Free Pascal: https://www.freepascal.org
- Eclipse: https://www.eclipse.org/
- Java Resources: https://docs.oracle.com/en/java/javase/14/docs/api/index.html
- Python Resources: https://docs.python.org/3/reference/
- Visual Studio Code: https://code.visualstudio.com/
Other Online Judges
- Codeforces: https://codeforces.com/ (Recommended)
- AtCoder: https://atcoder.jp/ (Recommended)
- HackerRank: https://www.hackerrank.com/ (Recommended)
- Sphere Online Judge: https://www.spoj.com/
- CodeChef: https://www.codechef.com/
- LeetCode: https://leetcode.com/
- Kattis: https://open.kattis.com/
- USACO Training Program Gateway: https://train.usaco.org/usacogate
- ACM Problem Set Archive: https://uva.onlinejudge.org/
- Peking University Online Judge: http://poj.org/