rifle1.rb

def is_single_riffle_recursive_optimized(half1, half2, shuffled_deck, shuffled_deck_index=0, half1_index=0, half2_index=0):
    # base case we've hit the end of shuffled_deck:
    if shuffled_deck_index + 1 > len(shuffled_deck):
        return True

    # if we still have cards in half1
    # and the "top" card in half1 is the same
    # as the top card in shuffled_deck
    if (not half1_index + 1 > len(half1)) and \
        half1[half1_index] == shuffled_deck[shuffled_deck_index]:
        half1_index += 1

    # if we still have cards in half2
    # and the "top" card in half2 is the same
    # as the top card in shuffled_deck
    elif (not half2_index + 1 > len(half2)) and \
        half2[half2_index] == shuffled_deck[shuffled_deck_index]:
        half2_index += 1

    # if the top card in shuffled_deck doesn't match the top
    # card in half1 or half2, this isn't a single riffle.
    else:
        return False

    # the current card in shuffled_deck has now been "accounted for."
    # so move on to the next one
    shuffled_deck_index+=1
    return is_single_riffle_recursive_optimized(half1, half2, shuffled_deck, shuffled_deck_index=shuffled_deck_index, half1_index=half1_index, half2_index=half2_index)