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
…
Example 1:
Input: “A”
Output: 1
Example 2:
Input: “AB”
Output: 28
Example 3:
Input: “ZY”
Output: 701

Runtime: 4 ms, faster than 70.01% of C++ online submissions for Excel Sheet Column Number.
Memory Usage: 7.7 MB, less than 100.00% of C++ online submissions for Excel Sheet Column Number.

class Solution {
public:
    int titleToNumber(string s) {
        int result = 0;
        for (int i = 0; i < s.size(); i++) {
            result = result * 26 + (s.at(i) - 'A' + 1);
        }
        return result;
    }
};