[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 pathSum(TreeNode *root, int sum, vector<int> & rec, vector<vector<int> >& res)
    {
        if(!root) return;
        rec.push_back(root->val);
        if(!root->left && !root->right)
        {
            if(root->val == sum)
            {
                res.push_back(rec);
                return;
            }
        }
        if(root->left)
        {
            pathSum(root->left, sum - root->val, rec, res);
            rec.pop_back();
        }
        if(root->right)
        {
            pathSum(root->right, sum - root->val, rec, res);
            rec.pop_back();
        }
    }
    vector<vector<int> > pathSum(TreeNode *root, int sum) 
    {
        vector<vector<int> > res;
        vector<int> rec;
        pathSum(root, sum, rec, res);
        return res;
    }
};