/**
* 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;
auto left=lowestCommonAncestor(root->left,p,q);
auto right=lowestCommonAncestor(root->right,p,q);
if(!left)return right;
if(!right)return left;
return root;//左右字数各有一个返回根节点;
}
};