1.Project Euler
https://projecteuler.net/
What is Project Euler?
Project Euler is a series of challenging mathematical/computer programming problems that will require more than just mathematical insights to solve. Although mathematics will help you arrive at elegant and efficient methods, the use of a computer and programming skills will be required to solve most problems.
The motivation for starting Project Euler, and its continuation, is to provide a platform for the inquiring mind to delve into unfamiliar areas and learn new concepts in a fun and recreational context.
2.Udacity
https://cn.udacity.com/
3.Coursera
https://www.coursera.org/
4.Codecademy
https://www.codecademy.com/
5.Khan Academy(可汗学院）
其中，Udacity和Coursera提供课程的付费版本。