leetcode之 Sum Root to Leaf Numbers

题目：

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

.

解答：

很简单的递归同时求和即可

/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int sum(TreeNode *root, int cur)
{
if(root->left == NULL && root->right == NULL)
return cur * 10 + root->val;
int lNum = 0;
int rNum = 0;
if(root->left)
lNum = sum(root->left, cur * 10 + root->val);
if(root->right)
rNum = sum(root->right, cur * 10 + root->val);
return lNum + rNum;
}
int sumNumbers(TreeNode* root) {
if(!root)
return 0;
return sum(root,0);
}
};