Links

Data structures and Algorithms

1. https://leetcode.com/
2. https://www.interviewbit.com/
3. https://www.hackerrank.com/
4. https://www.codechef.com/
5. https://www.spoj.com/
6. https://www.hackerearth.com/

Big-O

1. https://www.bigocheatsheet.com/

Hack Quests

1. https://overthewire.org/
2. https://www.vulnhub.com/
3. https://lab.pentestit.ru/
4. https://app.hackthebox.eu/home
5. https://pwnable.kr/index.php
6. https://www.root-me.org/
7. https://microcorruption.com/

Assembler

1. https://ravesli.com/uroki-assemblera/

Math

1. https://mathstudy.online/highmath
2. http://mathprofi.ru/
3. https://www.math10.com/ru/vysshaya-matematika/

Pattern

1. https://github.com/iluwatar/java-design-patterns

Java

1. https://medium.com/issuehunt/50-top-java-projects-on-github-adbfe9f67dbc
2. https://github.com/Vedenin/useful-java-links/tree/master/link-rus