Use a balanced stack: 1–2 challenge sites for problem‑solving, 1 project‑based platform to build deployable apps, and 1 portfolio‑friendly site to showcase work; practice daily, ship weekly.
Interview and problem‑solving
- LeetCode: the standard for interview prep with company‑tagged questions, contests, and discussions; great for mastering arrays, graphs, DP, and SQL.
- HackerRank and HackerEarth: curated domains and interview kits plus regular challenges; useful to warm up across languages and topics.
- Codeforces and AtCoder: frequent rated contests to sharpen speed and accuracy; ideal for competitive programming practice.
Learn by building projects
- freeCodeCamp: free, project‑first curriculum with certificates; each section ends with portfolio‑ready projects you can publish.
- The Odin Project: open‑source, full‑stack path (HTML/CSS/JS, Node/React) with strong community support; highly project‑oriented.
- Codecademy: interactive tracks with portfolio projects and instant feedback; use Pro for guided career paths.
Language practice with mentorship feel
- Exercism: mentor‑reviewed exercises across 70+ languages; great for idiomatic code and feedback loops.
- Codewars: kata with rankings to build fluency and pattern recognition in multiple languages.
Data, SQL, and analytics
- LeetCode SQL and HackerRank SQL tracks: realistic query practice with joins, windows, and CTEs; common in screenings.
- freeCodeCamp Data Analysis: pandas/visualization projects to turn raw data into dashboards and reports.
Competitive and gamified options
- CodeChef and TopCoder: monthly contests (Long, Cook‑Off, SRMs) for sustained problem‑solving under pressure.
- CodinGame: visual puzzles and multiplayer challenges that make algorithms fun and memorable.
How to turn practice into offers
- Weekly shipping: pick one small feature to build and deploy each week from lessons learned on challenge sites; link repos and demos.
- Portfolio polish: every project gets a README, test/CI badge, short demo video, and one measurable result (e.g., p95 latency improvement or dashboard insight).
- Blended routine: 30–45 minutes of challenges daily + a 2–3 hour weekend session to ship a feature on a real app; revisit problems to write cleaner solutions.
Quick starter bundles (pick one)
- Web/full‑stack: freeCodeCamp or Odin Project + Codewars warm‑ups + LeetCode weekly contest.
- Data/analytics: freeCodeCamp data path + LeetCode SQL + one monthly dashboard project.
- Competitive track: Codeforces/AtCoder contests + Codewars fluency + occasional HackerRank kits.
Bottom line: mix challenge platforms (LeetCode/Codeforces/Exercism) with project‑driven sites (freeCodeCamp/Odin/Codecademy), then package outputs into deployable repos and short demos—this combination builds skills that recruiters can verify quickly.