171 Excel Sheet Column Number

来源：Leetcode

原帖：https://oj.leetcode.com/problems/excel-sheet-column-number/

题目：
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

代码：

 class Solution {  
 public:  
   int titleToNumber(string s) { // 26进制转化为10进制  
     int num = 0;  
     for(auto i : s)  
       num = 26 * num + i-'A'+1;  
     return num;  
   }  
 };