Leetcode 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

解题思路：

很容易发现规律，例如AB = ('A'-'A' + 1) * 26 + (B-'A'+1)

Java code:

public int titleToNumber(String s) {
if(s == null) {
return 0;
}
int sum = 0;
for(int i = 0; i < s.length(); i++) {
sum += (s.charAt(i) - 'A' + 1) * Math.pow(26, s.length()-1-i);
}
return sum;
}