11. HackerEarth 1️⃣Practice 2️⃣Compete 12. CodeChef 1️⃣Learn 2️⃣Practice 3️⃣Compete 13. CodeForces 1️⃣Problem Set 2️⃣Contests 14. AtCoder 1️⃣Contest 15. Sphere Online Judge (SPOJ) 1️⃣Problems 2️⃣Contests 16. LightOJ 1️⃣Prob...