leetcode path sum II

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
vector<int>v1;
vector<vector<int>>v;
int countsum;
    vector<vector<int> > pathSum(TreeNode *root, int sum) 
    {
        v.clear();
        v1.clear();
        if(root==NULL)return v;    
        countsum=0;
        calsum(root,sum);
        return v;        
    }
    void calsum(TreeNode *root,int &sum)
    {
        if(root)
        {
            countsum+=root->val;
            v1.push_back(root->val);
        }
        if(countsum==sum&&root->left==NULL&&root->right==NULL)
        {
            v.push_back(v1);
        }     
        if(root)
        {
          if(root->left)calsum(root->left,sum);
          if(root->right)calsum(root->right,sum);
          countsum-=root->val;
          v1.pop_back();  
        }
    }
};