* Sync recent changes to the revised Word.
* Revised the preface chapter
* Revised the introduction chapter
* Revised the computation complexity chapter
* Revised the chapter data structure
* Revised the chapter array and linked list
* Revised the chapter stack and queue
* Revised the chapter hashing
* Revised the chapter tree
* Revised the chapter heap
* Revised the chapter graph
* Revised the chapter searching
* Reivised the sorting chapter
* Revised the divide and conquer chapter
* Revised the chapter backtacking
* Revised the DP chapter
* Revised the greedy chapter
* Revised the appendix chapter
* Revised the preface chapter doubly
* Revised the figures
* Add the chapter of divide and conquer.
Add the section of divide and conquer algorithm.
Add the section of build tree problem.
* Update build_tree.py
Yudong Jin