171. Excel Sheet Column Number

A -> 1
B -> 2
C -> 3
...
Z -> 26
AA -> 27

public class Solution {
public int titleToNumber(String s) {
//ABC -- C:3 + B:2*26 + A:1*26*26
int base=1; int result=0;
for(int i=s.length()-1; i>=0; i--){
result+=(s.charAt(i)-'A'+1)*base;
base*=26;
}
return result;
}
}