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 

Credits:
Special thanks to @ts for adding this problem and creating all test cases.

Understand the problem:
This question is an reverse question of the previous one. Let's still an transforming 26-base number to a 10-base number. Before we solve this question, let's consider how to convert a string to a number. For e.g. "123" -> 123, we start from the most significant digit,
1 + result * 10 = 1
2 + rssult * 10 = 12
3 + result * 10 = 123

So the solution here is the same, except for replacing the 10 by 26. Also noted that we need to add number by 1 each time since this question is index-1 started. 

Code (Java):

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