1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
class Solution {
public:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        if(root == NULL)  return NULL;
        if(root == p || root == q)   return root;     //返回p或q,只要发现一个就返回
            
        TreeNode* left =  lowestCommonAncestor(root->left, p, q);
        TreeNode* right = lowestCommonAncestor(root->right, p, q);
       
        if(left == NULL)    return right;
        if(right == NULL)   return left;      
        if(left && right)   return root;
        
        return NULL; // 
    }
};