PLEASE DO NOT USE ARRAY'S!

A DNA strand can be represented as a String of characters, where each character represents one of four nucleotide molecules: Adenosine, Cytosine, Guanine, and Thymine. The DNA strand contains only these four letters, but may have an arbitrary length. The complement of a DNA strand consists of another sequence of nucleotide molecules, except this time, every nucleotide in the original strand is replaced with a specific different nucleotide. Every Adenosine nucleotide is replaced by a Thymine (and vice