leetcode-129. Sum Root to Leaf Numbers

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.

思路：递归，每个节点保存临时和结果，遇到叶子节点就加入总和。

Acceped Code：

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 private:
12     int sum;
13 public:
14     int sumNumbers(TreeNode* root) {
15         sum=0;
16         if(root==nullptr)
17         return 0;
18         dfs(root,0);
19         return sum;
20     }
21     
22     void dfs(TreeNode* root,int presum)
23     {
24         if(root==nullptr)
25         return;
26         if(root->left==nullptr&&root->right==nullptr)
27         {
28             sum+=(presum*10+root->val);
29         }else
30         {
31             int temp=presum*10+root->val;
32             dfs(root->left,temp);
33             dfs(root->right,temp);
34         }
35     }
36 };

leetcode-129. Sum Root to Leaf Numbers

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