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]
]

 1 /**
 2  * Definition for binary tree
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Solution {
11     ArrayList<ArrayList<Integer>> result = null;
12     public ArrayList<ArrayList<Integer>> pathSum(TreeNode root, int sum) {
13         // IMPORTANT: Please reset any member data you declared, as
14         // the same Solution instance will be reused for each test case.
15         result = new ArrayList<ArrayList<Integer>>();
16         check(root, sum, new ArrayList<Integer>());
17         return result;
18     }
19     public void check(TreeNode root, int sum, ArrayList<Integer> row){
20         if(root == null) return;
21         row.add(root.val);
22         sum -= root.val;
23         if(root.left == null && root.right == null){
24             if(sum == 0)
25                 result.add(row);
26             return;
27         }
28         check(root.left , sum, new ArrayList<Integer>(row));
29         check(root.right, sum, new ArrayList<Integer>(row));
30     }
31 }