import time


def maintain_answer_time(create_time, update_time):
	"""
	Calculate the time that user maintains answer.
	:param create_time: '2019-04-09 00:00:00'
	:param update_time: '2019-04-09 00:00:00'
	:return: interval(s)
	"""
	create_t = [time.mktime(time.strptime(ct, '%Y-%m-%d %H:%M:%S')) for ct in create_time]
	update_t = [time.mktime(time.strptime(ut, '%Y-%m-%d %H:%M:%S')) for ut in update_time]

	interval = []
	for x, y in zip(update_t, create_t):
		interval.append(x - y)

	return interval