leetcode-171-excel sheet column number

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 

简单的26进制转化问题。

class Solution {
    public:
        int titleToNumber(string s) {
            int res=0;
            int high=s.length()-1;
            for(int i=0;i<s.length();i++)
                res+=pow(26,high-i)*(s[i]-'A'+1);

            return res;

        }
};