Excel Sheet Column Number.java

/*
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

time = O(n) the length of string
space = O(1)
*/

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