Sum Root to Leaf Numbers

1. Title

Sum Root to Leaf Numbers

2.   Http address

https://leetcode.com/problems/sum-root-to-leaf-numbers/

3. The question

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.

An example is the root-to-leaf path 1->2->3 which represents the number 123.

Find the total sum of all root-to-leaf numbers.

For example,

    1
   / 
  2   3

The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.

Return the sum = 12 + 13 = 25.

4. My code(AC)

public  static void  DFS(TreeNode root, String str)
    {
        if( root == null)
                return;
        if( root.left == null && root.right == null)
        {
            sum += Integer.parseInt(str + root.val);
            return;
        }

        DFS(root.right, str + root.val);
        DFS(root.left, str + root.val);

    }
    //Accepted
    public static int sumNumbers(TreeNode root) {

            DFS(root,"");
        return sum;

    }