/**
 * 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 == NULL){
            return NULL;
        }
        
        if(root->val == p->val || root->val == q->val){
            return root;
        }
        
        TreeNode* left = lowestCommonAncestor(root->left, p, q);
        TreeNode* right = lowestCommonAncestor(root->right, p ,q);
        
        if(left==NULL && right==NULL) return NULL;
        else if(left==NULL && right!=NULL) return right;
        else if(left!=NULL && right == NULL) return left;
        return root;
    }
};