171. Excel Sheet Column Number

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

 

//26进制转化成10进制 Time: O(n), Space: (1) 
   public int titleToNumber(String s) {
        if (s == null || s.length() == 0) {
            return 0;
        }
        
        int result = 0;
        
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            result = result * 26 + c - 'A' + 1;
        }
        
        return result;
    }