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 }

 

posted @ 2015-03-19 16:23  pku_smile  阅读(141)  评论(0)    收藏  举报