路径和 二叉树 leecode

题目不难，很快ac,纯粹靠手感。https://oj.leetcode.com/problems/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 {
     private int sum=0;
     public int sumNumbers(TreeNode root) {
         if(root==null) return 0;

         sum(root,""+root.val);
         return sum;

     }
     public void sum(TreeNode root,String s)
     {

         if(root.left==null&&root.right==null)
         {
             sum+=Integer.parseInt(s);
         }
         else
         {
             if(root.left!=null) sum(root.left,s+root.left.val);
             if(root.right!=null) sum(root.right,s+root.right.val);

         }

     }

 }