Update problem-sets-competitive-programming.md

problem-sets-competitive-programming.md

@@ -53,6 +53,7 @@
 * [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)