Some time ago I did a lot of Codewars in my spare time. It's a great platform with loads of challenges in different languages, a nice reward system to motivate you (you earn Kata as you go), with options to compare your solutions and overall a great community.

I would especially recommend it for job-seeking phase as it's a great way to practice appliance of data structures and algorithms to community created and curated theoretical problems.

Some other awesome coding challenge sites include HarckerRank, LeetCode, CodeChef, Coderbyte, TopCoder, Exercism.io, Project Euler and many others.

For more practical challenges I would recommend amazing recent project devchallenges.io. Here's the story of how it came to life: link.

Have you tried any of these and what's your experience?