in this one I think you would start by ckecking if s1==s2. If it is not, I guess you could limit s2 to however many chars s1 has, and see if they match. If they dont, you could remove the first char from s2, and recheck to see if the second way works again. If you contiued doing that until s2 was the same amount of chars as s1, you would know whether or not it was possible.