/**
 * 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) {
        //树嘛，得想到递归，lowestCommonAncestor函数实现的功能是找到两个节点的公共
        //父节点，如果未找到则返回本身
        if(!root) return nullptr;
        if(root == p || root == q) return root;
        auto left = lowestCommonAncestor(root->left,p,q);
        auto right = lowestCommonAncestor(root->right,p,q);

        if(left && right) return root;  //如果两边都有公共节点，说明两边都是他本身，返回root
        if(right) return right; //如果只有一边有则返回那一边即可
        return left;
    }
};