681.py

'''
Given a time represented in the format "HH:MM", form the next closest time by reusing the current digits. There is no limit on how many times a digit can be reused.

You may assume the given input string is always valid. For example, "01:34", "12:09" are all valid. "1:34", "12:9" are all invalid.

Example 1:

Input: "19:34"
Output: "19:39"
Explanation: The next closest time choosing from digits 1, 9, 3, 4, is 19:39, which occurs 5 minutes later.  It is not 19:33, because this occurs 23 hours and 59 minutes later.
Example 2:

Input: "23:59"
Output: "22:22"
Explanation: The next closest time choosing from digits 2, 3, 5, 9, is 22:22. It may be assumed that the returned time is next day's time since it is smaller than the input time numerically.
'''

class Solution(object):
    def nextClosestTime(self, time):
    	current_time = 60*int(time[:2]) + int(time[3:])
    	allowed = {int(x) for x in time if x != ':'}
    	result = 24*60
    	ans = current_time
    	for h1, h2, m1, m2 in itertools.product(allowed, repeat=4):
    		hours, minutes = 10*h1+h2, 10*m1+m2
    		if hours < 24 and minutes < 60:
    			elapsed = 60*hours + minutes
    			diff = (current_time - elapsed)%(24*60)
    			if 0 < diff < result:
    				result = diff
    				ans = elapsed

    	return "{:02d}:{:02d}".format(divmod(ans, 60))