leetcode-Path Sum II

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 and 

sum
= 22

,

5
/ \
4   8
/   / \
11  13  4
/  \    / \
7    2  5   1

return

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

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
void Path(TreeNode *node, int num, vector<int> a, vector<vector<int> > &ret)
{
if(node == NULL)return;
a.push_back(node->val);
if((node->val == num)&&(node->left == NULL)&&(node->right == NULL))
{
ret.push_back(a);
return;
}
Path(node->left,num - node->val,a,ret);
Path(node->right,num - node->val,a,ret);
return;
}

vector<vector<int> > pathSum(TreeNode *root, int sum) {
vector<vector<int> > ret;
vector<int> a;
Path(root,sum,a,ret);
return ret;
}
};