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
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    ArrayList<ArrayList<Integer>> result = null;
    public ArrayList<ArrayList<Integer>> pathSum(TreeNode root, int sum) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        result = new ArrayList<ArrayList<Integer>>();
        check(root, sum, new ArrayList<Integer>());
        return result;
    }
    public void check(TreeNode root, int sum, ArrayList<Integer> row){
        if(root == null) return;
        row.add(root.val);
        sum -= root.val;
        if(root.left == null && root.right == null){
            if(sum == 0)
                result.add(row);
            return;
        }
        check(root.left , sum, new ArrayList<Integer>(row));
        check(root.right, sum, new ArrayList<Integer>(row));
    }
}