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

.

参考了别人的答案，发现也不很难。对二叉树的递归定义理解还是不够。

/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int sumNumbers(TreeNode *root) {
return sumCal(root,0);

}

int sumCal(TreeNode * root,int sum)
{
if(root == 0)
return 0;
if(root -> left == 0 && root -> right == 0)
return sum * 10 + root ->val;

return sumCal(root->left,sum * 10 + root ->val)+sumCal(root->right,sum * 10 + root ->val);
}
};