Start to review some college stuff.

For some reason, I found in day-to-day work, I focused on too much RAD (Rapid Application Development) , and I lost some ability to write some simple data structure code.

I guess many developers nowadays rely too much on libraries, without enough attention paid to how those libraries were actually develped.

I think I need some time to review some basic codes like how to write some basic data structure and their operations.
1. link list.
2. stack.
3. queue.
4. tree.
5. graph.