Encrypt

For the following decoding problem, assume all alphanumeric characters are
arranged in a square matrix as follows:

A B C D E F
G H I J K L
M N O P Q R
S T U V W X
Y Z 0 1 2 3
4 5 6 7 8 9

Given a two character string, the string is encoded according to an algorithm
called encrypt(String). The way it works is if the two characters are in the
same row, the string that is returned is the reverse of those two characters.
Otherwise, the string returned is the two characters that would be needed to
complete a rectangle, from top to bottom. Here are a few examples:

TW -> WT
BQ -> EN
S9 -> X4


Create a class Encrypt that contains this encrypt method. Assume that the only
allowable input are the alphanumeric characters in the matrix above (no
lowercase letters, no spaces, no punctuation marks). 

Here is the method signature (be sure your method is public):
String encrypt(String input)