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 

解析：

实际上就是26进制，自己写的：

class Solution {
public:
    int titleToNumber(string s) {
        int n = 0;
        for(int i = s.size()-1,j = 0; i >= 0; i--,j++)
            n += (int(s[i])-64) * pow(26,j);
        return n;
    }
};