Function practice

practice(day: number, buckets: Set<Flashcard>[], retiredBucket: number): Flashcard[]
Generate a sequence of flashcards for practice on a particular day.

Returns
a sequence of flashcards such that a card appears in the sequence if and only if its bucket number is some i < retiredBucket such that day is divisible by 2^i
Parameters
- day: number
  
  day of the learning process. Must be integer >= 1.
- buckets: Set<Flashcard>[]
  
  a list of disjoint sets representing learning buckets, where buckets[i] is the set of cards in the ith bucket for all 0 <= i <= retiredBucket
- retiredBucket: number
  
  number of retired bucket. Must be an integer >= 0.
Returns Flashcard[]