Path Sum II

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    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.
        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
        if(root == null) return result;
        helpler(result, new ArrayList<Integer>(), root, sum);
        return result;
    }
        private void helpler(ArrayList<ArrayList<Integer>> result, ArrayList<Integer> paths, TreeNode root, int sum)
    {
        if(root == null) return;
        paths.add(root.val);
        if(root.left == null && root.right == null && root.val == sum)
        {
            ArrayList<Integer> temp = new ArrayList<Integer>(paths); //has to copy, or will cause the Output Limit Exceeded error
            result.add(temp);
        }
        else{
            helpler(result, paths, root.left, sum-root.val);
            helpler(result, paths, root.right, sum-root.val);
        }
        paths.remove(paths.size()-1);
    }
}