1. HackerRank: HackerRank is one of the most popular coding challenge websites with a vast array of challenges over 1,000 coding challenges in more than 30 programming languages. It offers a good mix of algorithmic and data structures problems, making it a well-rounded platform for developers of all levels. HackerRank also has a strong focus on interview preparation, with features like mock interviews and company-specific challenges.
2. LeetCode: LeetCode is another popular website known for its focus on algorithms and data structures problems. It has over 1,900 problems categorized by difficulty and topic, making it a great resource for targeted practice. LeetCode is also known for its active community forums, where you can get help with problems and discuss solutions with other coders.