1. Given a list of words, return an array which indicates the frequency that
each letter occurs. For example, in the list ["apple", "bob"], [ 'a' -> 1,
'b'->2, 'e'->1, 'l'->1, 'o'->, 'p'->2] . The order of the array does not
matter and a Frequency class will be provided.
2. Given a list of words, indicate whether the list constitutes a "Word Lad-
der." Return a True or False (Boolean) A Word Ladder is a series of words where each succeeding word
changes by only one letter. You may not assume that all words will be of
the same length, and you may not assume the length of the list.
3. Given an integer greater than 2, X, return an array populated with all
prime numbers up to and including X.