LeetCode: 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 

class Solution {public:    int titleToNumber(string s) {        int result = 0;        int multi = 1;        for(int i = s.size() -1; i >= 0; i--)        {            result += (s[i]-64) * multi;            multi *= 26;        }        return result;    }};

Round 3:

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