All it does is start from right to left, grabbing every 3 digits and pushing them into a chunks array.

We then adjust for the scale we're at, and make sure we have enough digits to justify that scale.

Now, here's the key. For each chunk, we process it in this manner:

1. Split it into individual integers ("123" becomes [1, 2, 3])
2. Add tens word if array item exists
3. Add 'and' string after units or tens integer (optional)
4. Add hundreds word if array item exists

Complexity of Final Solution

Let n be the number of digits in the input num. We iterate through the string equivalent of num, and examining 3 digits at a time for O(n) linear time complexity. When converting nums to a string of length n, we have O(n) space complexity.