算法演绎:
http://code.jcly.twbbs.org/docs/algorithm/%E6%BC%94%E7%AE%97%E6%B3%95%E7%AD%86%E8%A8%98/www.csie.ntnu.edu.tw/_u91029/Tree.html
Top-Down Approach
and A Bottom-up Approach
http://leetcode.com/2011/07/lowest-common-ancestor-of-a-binary-tree-part-i.html
原文：http://www.cnblogs.com/leetcode/p/3667797.html