path-sum-ii leetcode C++

Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.

For example: Given the below binary tree andsum = 22, 5 / 
4 8 / / 
11 13 4 / / 
7 2 5 1 return

[ [5,4,11,2], [5,8,4,5] ]

C++

/**
 * 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<vector<int> > pathSum(TreeNode *root, int sum) {
        vector<vector<int>> dp;
        vector<int> path;
        getPath(root,sum,dp,path);
        return dp;
    }
    void getPath(TreeNode *root, int sum,vector<vector<int>>& dp,vector<int> path){
        if(NULL == root) return;
        path.push_back(root->val);
        if(NULL == root->left && NULL == root->right && root->val == sum )
            dp.push_back(path);
        getPath(root->left,sum - root->val,dp,path);
        getPath(root->right,sum - root->val,dp,path);
    }
};