A string s is said to be periodic with a period α, if s is α^{k} for some k > 2. (Note that α^{k} is the string formed by concatenating k times.) A DNA sequence s is called a tandem repeat if it is periodic. Given a DNA sequence s, determine if it is periodic, and if so, the values for and k. Note that there could be more than one period for a periodic string. In such a case, you need to report the shortest period.