LeetCode: 171 Excel Sheet Column Number(easy)

题目：

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 

代码：

class Solution {
public:
    int titleToNumber(string s) {
        map<char, int> map;
        int num = 1;
        int result = 0;
        for (char i = 'A'; i<='Z'; i++){
            map[i] = num;
            num++;
        }
        int j = 0;
        for(auto c = s.crbegin(); c<s.crend(); c++){
            result = map[*c]*pow(26, j) + result;
            j++;
        }
            
        return result;
    }
};