leetcode------Sum Root to Leaf Numbers

标题：	Sum Root to Leaf Numbers
通过率：	30.4%
难度：	中等

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.

整个过程是深度优先，然后每下一层就放大十倍，那么如果是叶子节点则与sum相加，其他时候继续往下搜索，代码如下：

 1 /**

 2  * Definition for binary tree

 3  * public class TreeNode {

 4  *     int val;

 5  *     TreeNode left;

 6  *     TreeNode right;

 7  *     TreeNode(int x) { val = x; }

 8  * }

 9  */

10 public class Solution {

11     int sum;

12     public int sumNumbers(TreeNode root) {

13         sum=0;

14         if(root==null)return 0;

15         dfs(root,0);

16         return sum;

17     }

18     public void dfs(TreeNode root,int num){

19         num=num*10+root.val;

20         if(root.right==null&&root.left==null) sum+=num;

21         if(root.left!=null) dfs(root.left,num);

22         if(root.right!=null) dfs(root.right,num);

23         

24     }

25 }