Subtask 1

Hard-code every possible string containing "a" and "b" of length between $2$ and $4$ (there are $30$ such strings) and output whether it alternates between heavy "a" and light "b" or heavy "b" and light "a".

Subtask 2

There was no intended solution for this subtask. It was intended to allow for possibly slower full solutions.

Subtask 3

We consider two cases for if it starts with "a" or not:

• Check that every second letter is "a" and that the rest are not "a".
• Check that every second letter is not "a" and that the rest are "a".

If either case is true, output T; otherwise, output F.

Subtask 4

First, create an array that will store the frequency of each letter in the string. Each element represents the count of a particular letter. Then, iterate over all letters in the string and increment the frequency of it in the array.

We realize we can extend the logic from subtask 3 with this array. If a letter has a frequency greater than $1$ in the array, it is heavy; if not, it is light.

We consider two cases for if it starts with a heavy letter or not:

• Check that every second letter has a frequency greater than $1$ and that the rest are light.
• Check that every second letter does not have a frequency greater than $1$ and that the rest are heavy.

If either case is true, output T; otherwise, output F.