### Index
* [Competitive Programming ](#competitive-programming )
* [CTF Capture the Flag ](#capture-the-flag )
* [Data science ](#data-science )
* [Information security ](#information-security )
* [Problem Sets ](#problem-sets )
### Competitive Programming
* [4Clojure ](http://www.4clojure.com )
* [A2 Online Judge ](https://a2oj.com )
* [AtCoder ](https://atcoder.jp )
* [Binary Search ](https://binarysearch.com )
* [Caribbean Online Judge ](http://coj.uci.cu )
* [COCI ](https://hsin.hr/coci/ )
* [Codeabbey ](http://www.codeabbey.com )
* [Codechef ](https://www.codechef.com/contests )
* [Codecombat ](https://codecombat.com )
* [Codeeval ](https://www.codeeval.com )
* [CodeFights ](https://codefights.com )
* [Codeforces ](http://codeforces.com/contests )
* [Coderbyte ](https://coderbyte.com )
* [Codewars ](http://www.codewars.com )
* [Codingame ](https://www.codingame.com/start )
* [E-olymp ](https://www.e-olymp.com/en/ )
* [Facebook Hackercup ](https://www.facebook.com/hackercup )
* [Google Code Jam ](https://codingcompetitions.withgoogle.com/codejam )
* [HackerEarth ](https://www.hackerearth.com )
* [Hackerrank ](https://www.hackerrank.com )
* [Internet Problem Solving Contest ](http://ipsc.ksp.sk )
* [Just another Golf Coding ](http://jagc.org )
* [Kattis ](https://open.kattis.com )
* [LeetCode ](https://leetcode.com )
* [Microcorruption ](https://microcorruption.com/login )
* [Sphere Online Judge ](http://www.spoj.com/contests )
* [Topcoder ](https://www.topcoder.com )
* [Toph ](https://toph.co )
* [URI Online Judge ](https://www.urionlinejudge.com.br/judge/en/login )
### Capture the flag
* [Google Ctf ](https://capturetheflag.withgoogle.com ) (email adress *requested* )
* [Hackthebox ](https://www.hackthebox.eu ) (email adress *requested* )
* [Overthewire Wargames fungame to practice CTF ](https://overthewire.org/wargames/bandit )
* [Picoctf ](https://picoctf.org/resources ) (email adress *requested* )
* [TryHackMe ](https://tryhackme.com ) (email adress *requested* )
### Data science
* [AIcrowd ](https://www.aicrowd.com )
* [DrivenData ](https://www.drivendata.org )
* [Kaggle ](https://www.kaggle.com )
### Information security
* [ångstromCTF ](https://angstromctf.com )
* [CTFtime ](https://ctftime.org )
### Problem Sets
* [500 Data structures and algorithms interview questions and their solutions in C++ ](https://techiedelight.quora.com/500-Data-structures-and-algorithms-interview-questions-and-their-solutions-in-C%2B%2B )
* [A2 Online Judge ](https://a2oj.com/ps )
* [Advent Of Code ](http://adventofcode.com )
* [Anarchy Golf ](http://golf.shinh.org )
* [CareerCup ](http://www.careercup.com )
* [CheckIO ](http://www.checkio.org )
* [Codeforces ](http://codeforces.com/problemset )
* [Codility ](https://codility.com/programmers/ )
* [Coding Bat ](http://codingbat.com/java )
* [CSES Problem Set ](https://cses.fi/problemset/ )
* [Exercism ](http://exercism.io )
* [Geeks For Geeks ](http://www.geeksforgeeks.org )
* [Google Code Jam - Practise ](https://code.google.com/codejam/contests.html )
* [Hacker.org ](http://www.hacker.org )
* [HackerEarth ](https://www.hackerearth.com )
* [HDU Online Judge ](http://acm.hdu.edu.cn )
* [Interactive Coding Challenge ](https://github.com/donnemartin/interactive-coding-challenges )
* [InterviewBit ](https://www.interviewbit.com )
* [Kattis ](https://open.kattis.com )
* [Leetcode ](https://leetcode.com )
* [Mathproblem of the Month - Bilkent University ](http://www.fen.bilkent.edu.tr/~cvmath/prob-month.html )
* [PEG Judge ](http://wcipeg.com )
* [PKU Online Judge ](http://poj.org )
* [Ponder This! ](https://www.research.ibm.com/haifa/ponderthis/index.shtml )
* [ProblemBook.NET ](https://github.com/AndreyAkinshin/ProblemBook.NET )
* [Project Euler ](https://projecteuler.net )
* [Python Practice Projects ](http://pythonpracticeprojects.com )
* [Rosalind ](http://rosalind.info/problems/locations/ )
* [Sphere Online Judge ](http://www.spoj.com/problems/classical )
* [TalentBuddy ](http://www.talentbuddy.co/blog/ )
* [Timus Online Judge ](http://acm.timus.ru )
* [URI Online Judge ](https://www.urionlinejudge.com.br/judge/login )
* [UVa Online Judge ](https://uva.onlinejudge.org/index.php?Itemid=8&option=com_onlinejudge )