Excel Sheet Column Number

lc 171

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 


```
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 

        public int titleToNumber(String s) {
        if( s == null || s.length() == 0) return 0;
          int res = 0;
          for(int i = 0; i < s.length(); i++){
            char cur = s.charAt(i);
            res = res * 26 +  (int)( cur - 'A' + 1);
          }
          return res;
        }