LeetCode-Excel Sheet Column Number

Description：

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 
...      

Example 1:

Input: “A”

Output: 1

Example 2:

Input: “AB”

Output: 28

Example 3:

Input: “ZY”

Output: 701

Java

class Solution {
    public int titleToNumber(String s) {
        int columnNumber = 0;
        int order = 1;
        for (int i = s.length() - 1; i >= 0; i--) {
            columnNumber += (s.charAt(i) - 'A' + 1) * order;
            order *= 26;
        }
        return columnNumber;
    }
}