Path Sum II

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<Integer> list = new ArrayList<Integer>();
        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
        if(root == null)
            return result;
        traversal(root, sum, list, result);
        return result;
    }
    
    private void traversal(TreeNode root, int sum, ArrayList<Integer> list, ArrayList<ArrayList<Integer>> result)
    {
        list.add(root.val);
        if(root.left == null && root.right == null){
            if(sum == root.val){
                ArrayList<Integer> tmp = new ArrayList<Integer>();
                tmp.addAll(list);
                result.add(tmp);
            }
        }
            
        if(root.left != null)
            traversal(root.left, sum - root.val, list, result);
        if(root.right != null)
            traversal(root.right, sum - root.val, list, result);
        list.remove(list.size() - 1);
    }
}