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]
]

Solution: DFS.

/**
 * 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> > res;
        vector<int> path; 
        pathSumRe(root, sum, path, res);
        return res;
    }
    
    void pathSumRe(TreeNode* root, int sum, vector<int> &path, vector<vector<int> > &res)
    {
        if(!root) return;
        if(!root->left && !root->right && sum == root->val) {
            path.push_back(sum);
            res.push_back(path);
            path.pop_back();
        }
        path.push_back(root->val);
        pathSumRe(root->left, sum-root->val, path, res);
        pathSumRe(root->right, sum-root->val, path, res);
        path.pop_back();
    }
};