一，OA1 - Debugging
http://www.jianshu.com/p/839a9268b687
二，OA2 - Reasioning
http://www.jianshu.com/p/af68de7b3638
三，概念题
http://www.jianshu.com/p/8b47023e473d
四，Leetcode算法
1，Binary search tree minimum sum from root to leaf
2，reverse second half of linked list
