LeetCode 0171 - Excel Sheet Column Number

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

Input: "A"
Output: 1

Input: "AB"
Output: 28

Input: "ZY"
Output: 701

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