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.

 

Analyse: DFS. Compute the left and right subtree of the root respectively and add them. 

Runtime: 4ms.

 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 public:
12     int sumNumbers(TreeNode* root) {
13         return dfs(root, 0);
14     }
15     int dfs(TreeNode* root, int sum){
16         if(!root) return 0;
17         if(!root->left && !root->right) return sum * 10 + root->val;
18         
19         return dfs(root->left, sum * 10 + root->val) +
20                dfs(root->right, sum * 10 + root->val);
21     }
22 };

 

posted @ 2015-08-02 21:35  amazingzoe  阅读(114)  评论(0)    收藏  举报