import collections


def duplicate_cards(tuple_of_cards):
    """Return a list of the cards that are duplicated in the tuple.

    If a card is duplicated N times, the card should be in the result N times
    so that the caller knows how many times it's been duplicated.

    If is_standard_deck() returns false for a list, this function may help the
    caller determine what's wrong with their deck of cards."""

    c = collections.Counter(tuple_of_cards)
    return [card for card in tuple_of_cards if c[card] > 1]