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 
...

Example 1:

Input: “A”
Output: 1
Example 2:

Input: “AB”
Output: 28
Example 3:

Input: “ZY”
Output: 701

C++
int titleToNumber(string s) {
        int n = 0;
        int len = s.size()-1;
        int res = 0;
        while(n <= len)
        {
            int temp = (int)(s[n] - 'A') + 1;
            res = res*26 + temp;
            n++;
        }
        return res;
    }