One tool of basic cryptanalysis is determining how frequently any letter occurs in a given passage. From there, one can often determine the characteristics of a substitution cipher. Return the letter and frequency of the most-frequently occurring letter in the input in the form "letter=frequency". If multiple letters have the same highest frequency, return the first of those in the alphabet. Precondition: str will only contain capital letters.

HINT

You will probably need multiple loops for this method. Consider what data structure is best to store the frequency information.