171. Excel Sheet Column Number (Math)

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

class Solution {
public:
    int titleToNumber(string s) {
        //the last bit of s, multiply 26
        //then left move 1 bit, multiply 26^2
        //iterate

        int len = s.length();
        int ret = ;
        int multiplier = ;
        int cur;
        for(int i = len-; i >= ; i--){
            cur = s[i]-'A'+;
            ret += cur*multiplier;
            multiplier *= ;

        }

        return ret;

    }
};