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 

                                                     

                                                    MY:

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

                                                                                 better answer

class Solution {
public:
    int titleToNumber(string s) {
        int result = 0;
        int pow = 26;
        for(char c : s)
        {
            result = result*pow + c - 'A' + 1;
        }
        
        return result;
    }
};