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) {
if (s.length() == 0 || s == null)
return 0;
int sum = 0;
for (int i = 0; i < s.length(); i++) {
sum = sum * 26 + (s.charAt(i) - 'A' + 1);
}
return sum;
}
}