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 

 1 class Solution {
 2 public:
 3     int titleToNumber(string s) {
 4         auto it = s.end()-1;
 5         char c;
 6         int num =0;
 7         int i=1;
 8         while(it>=s.begin()) {
 9             c = *it;
10             num += (c-'A'+1)*i;
11             i *= 26;
12             --it;
13         }
14         return num;
15     }
16 };

模仿整数的操作即可。