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) {
if(s.size() <= 0) return 0;
int col = s[0] - 'A' + 1;
for(int i=1;i<s.size();i++){
col = col * 26 + s[i] - 'A' + 1;
}
return col;
}
};
