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CodeWars

Pros:

• Interesting terms motivate you
• Levels and points
• Saves your solutions
• Really fun warrior idea
• Easy to get the hang of
• Markdown badge api and code ready
• Huge variety of languages
• (BIG) dark ui supported

Cons:

• No comparison of solution submission: speed, memory usage, best practice etc. not tracked.
• Doesn't feel professional
• Problems doesn't feel realistic, these won't come up on interviews probably.

LeetCode

Pros:

• Overall more professional
• Could be used as a validation of your skills
• Realistic problems
• Comparison and analytics about your solution's speed, memory usage. Tells you that your solution was better than x% of users.
• Geared towards interview preperation

Cons:

• No badge for markdown, pepehands.
• No dark/night mode for UI. Hurts your soul.

[hackerrank] (https://www.hackerrank.com)

Pros:

• Professional, and promising look that it'll be usefull for landing a job. ?
• Achievements
• Many sets of preparation material

Cons:

• Terrible problem explanations. Had a hard time understanding even the simplest questions.

Haven't tried yet

• https://www.hackerrank.com/ (in progress)
• https://exercism.io/
• https://www.codingame.com/
• https://app.codility.com/programmers/challenges/
• https://www.codechef.com/
• https://codingbat.com/ //Java and python