Question

Input Value can be from A to ZZZ (only alphabetical, no numeric characters) how can I validate a from and to field.

Where the input can be A or AA or AAA

• B > A
• BB > A
• BBB > A
• BBB < B
• BBB < BB
• DD > C
  but then D should be < CC fails because it is not a lexicographical order

I was thinking check the length first because if the from length is less than to length then it will always be less. If equal in length then an alphabetical check. Then I come unstuck.

Not simple lexicographical order because three possiable groups single, double, triple chars single group lower than double and triple group and double lower than triple group not just alphabetical.

Answer 1

You can do the following: Imagine the String AAA as a number, saying A*26^2 + A*26^1 + A*26^0

(Base 26, because there are that much letters)

Split the String, Cast values A to Z to 1 to 26 (WhiteSpace in front = 0) and you are done:

 A = 0*26^2 + 0*26^1 + 1*26^0 => 1
 B = 2 => 2
 ...
 Z = 26 => 26
 AA = 1 * 26^1 + 1 => 27
 ...
 ZZ = 26*26^1 + 26 = 702
 ...
 ZZZ = 26*26^2 + 26*26^1 + 26 => 18278 

wrap it Like

    public int LetterCodeToInt(String LetterCode)
    {
        //fill up whitespaces in front.
        String s = LetterCode.PadLeft(3, '_').ToUpper();

        int value = 0;
        int k = s.Length -1;
        for (int i = 0; i < s.Length; i++)
        {
            if (s[i] != '_')
            {
                //ASCII "A" is 65, subtract 64 to make it "1" 
                value += (((int)s[i]) - 64) * Convert.ToInt32(Math.Pow(26, k));
            }
            k--;
        }
        return value;
    }

and you can do:

 if (LetterCodeToInt("AAA") > LetterCodeToInt("AZ")){

 }