235. Lowest Common Ancestor of a Binary Search Tree

题目来源【Leetcode】

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.

这道题是找两个结点最近的公共祖先，直接根据BST的性质进行分类即可：

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {        if(!root || p == root || q == root) return root;        if(p->val < root->val && q->val < root->val) return lowestCommonAncestor(root->left, p, q);        if(p->val > root->val && q->val > root->val) return lowestCommonAncestor(root->right, p, q);        return root;    }};