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.
基本题：
int sumNumbers(TreeNode* root)
{
int total=0;
calSum(root,total,0);
return total;
}
void calSum(TreeNode* root,int& tot,int cur)
{
if (!root)
return;
cur=cur*10+root->val;
if (!root->left&&!root->right)
{
tot+=cur;
return;
}
if(root->left)
calSum(root->left,tot,cur);
if(root->right)
calSum(root->right,tot,cur);
}