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 = ;
int result = ;
for (char i = 'A'; i<='Z'; i++){
map[i] = num;
num++;
}
int j = ;
for(auto c = s.crbegin(); c<s.crend(); c++){
result = map[*c]*pow(, j) + result;
j++;
}
return result;
}
};