Difficulty：Easy
Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.
According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes v and w as the lowest node in T that has both v and w as descendants (where we allow a node to be a descendant of itself).”

For example, the lowest common ancestor (LCA) of nodes 2 and 8 is 6. Another example is LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.
思路
首先要理解BST的概念，即对于某一节点root的值，肯定大于其左侧树所有节点的值，而小于右侧数所有节点的值。这样就可以通过比较val来找到目标。
坑
一开始没有get到BST的精髓，起码被坑了3个小时。
代码

原题链接：https://leetcode.com/problems/lowestcommonancestorofabinarysearchtree/