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 sub(vector<vector<int> >& ret,vector<int>& val,TreeNode *root,int sum){
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(root==NULL)return;
        if(root->left==NULL&&root->right==NULL){
            //leaf
            if(root->val==sum){
                val.push_back(root->val);
                ret.push_back(val);
                val.pop_back();
            }
            else return;
        }
        else{
           val.push_back(root->val);
           sub(ret,val,root->left,sum-root->val);
           sub(ret,val,root->right,sum-root->val);
           val.pop_back();
        }
    }
    vector<vector<int> > pathSum(TreeNode *root, int sum) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<vector<int> > ret;
        vector<int> val;
        sub(ret,val,root,sum);
        return ret;
    }
};