path sum II

/**
 * 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:
    vector<vector<int>> pathSum(TreeNode* root, int sum) {
        vector<vector<int>> vv,vv2;
        
        if(root==NULL) return vv;
        vector<int> v;
          
        if(root->left ==NULL && root->right == NULL) {
            if(root->val==sum){
                v.push_back(root->val);
                vv.push_back(v);
            }
            return vv;
        }
            
        vv = pathSum(root->left,sum-root->val);
        if(!vv.empty()){
            for(int i=0;i<vv.size();i++){
                vv[i].insert(vv[i].begin(),root->val);
            }
        }
       
        vv2 = pathSum(root->right,sum-root->val);
        if(!vv2.empty()){
            for(int i=0;i<vv2.size();i++){
                vv2[i].insert(vv2[i].begin(),root->val);
                vv.push_back(vv2[i]);
            }
        }
        
        return vv;
    }
};