171. Excel Sheet Column Number

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

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