235. 二叉搜索树的最近公共祖先

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution 
11 {
12 public:
13     TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) 
14     {
15         if(p == root || q == root || !root) return root;
16 
17         TreeNode* a = lowestCommonAncestor(root->left,p,q);
18         TreeNode* b = lowestCommonAncestor(root->right,p,q);
19         if(!a && b) return b;
20         else if(a && !b) return a;
21         else if(a && b) return root;
22         else return NULL;
23     }
24 };