Next Closest Time

 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):
        cur = 60 * int(time[:2]) + int(time[3:])
        allowed = {int(x) for x in time if x != ':'}
        while True:
            cur = (cur + 1) % (24 * 60)
            if all(digit in allowed
                    for block in divmod(cur, 60)
                    for digit in divmod(block, 10)):
                return "{:02d}:{:02d}".format(*divmod(cur, 60))

TC : O(1) max 24*60 iterations

SC : O(1)