Algorytmika

https://www.nsa.gov/news-features/puzzles-activities/
https://www.hackerrank.com/domains/algorithms/implementation
http://codeforces.com/
https://www.hackerrank.com
https://www.codingame.com/
https://projecteuler.net/archives
http://solve.edu.pl/~sparingi/
https://leetcode.com/
http://www.geeksforgeeks.org/
http://www.lintcode.com/en/
http://blog.gainlo.co
http://horicky.blogspot.com
https://www.hiredintech.com/classrooms/system-design/lesson/52
http://www.lecloud.net/tagged/scalability
http://tutorials.jenkov.com/software-architecture/index.html
http://highscalability.com/
https://medium.com/@XiaohanZeng/i-interviewed-at-five-top-companies-in-silicon-valley-in-five-days-and-luckily-got-five-job-offers-25178cf74e0f

(Polish speaking)

http://www.rafalnowak.pl/wiki/


https://sio2.mimuw.edu.pl/c/pa-2015-1/p/sia/