HackerRank

LeetCode is the most popular platform for practicing coding problems, preparing for technical interviews, and improving algorithm skills.

CodeChef is a competitive programming platform hosting contests, practice problems, and a learning community for programmers.

Codeforces is a competitive programming website where users participate in contests and solve algorithmic problems with real-time rankings.

GeeksforGeeks is a comprehensive learning platform for programming, algorithms, data structures, and interview preparation.

InterviewBit helps you prepare for coding interviews with curated problems, mock interviews, and company-specific prep materials.

TopCoder is one of the first competitive programming platforms offering contests, challenges, and freelance opportunities for developers.