Excel Sheet Column Number

Related to question Excel Sheet Column Title

Given a column title as appear in an Excel sheet, return its corresponding column number.

For example:

    A -> 1
    B -> 2
    C -> 3
    ...
    Z -> 26
    AA -> 27
    AB -> 28 

 class Solution {
 public:
     int titleToNumber(string s) {
         auto it = s.end()-;
         char c;
         int num =;
         int i=;
         while(it>=s.begin()) {
             c = *it;
             num += (c-'A'+)*i;
             i *= ;
             --it;
         }
         return num;
     }
 };

模仿整数的操作即可。