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

相当于26进制的运算：

int titleToNumber(char *s) {
   int i,res=0;
   for(i = 0; i<strlen(s); i++){
       res = res*26+s[i]-'A'+1;
   }
   return res;
}