Sum Root to Leaf Numbers

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int sumNumbers(TreeNode root) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        ArrayList<Integer> result = new ArrayList<Integer>();
        if(root == null)
            return 0;
        dfs(result, 0, root);
        int sum = 0;
        for(int i:result)
            sum += i;
        return sum;
    }
    
    private void dfs(ArrayList<Integer> result, int now, TreeNode root){
        if(root.left == null && root.right == null){
            result.add(10*now+root.val);
            return;
        }
        now = now * 10 + root.val;
        if(root.left!=null)
            dfs(result, now, root.left);
        if(root.right!=null)
            dfs(result, now, root.right);
    }
}