108.py

class Solution(object):
    def nextClosestTime(self, time):
        """
        :type time: str
        :rtype: str
        """
        hour, minute = time.split(":")

        # Generate all possible 2 digit values
        # There are at most 16 sorted values here
        nums = sorted(set(hour + minute))
        two_digit_values = [a + b for a in nums for b in nums]

        # Check if the next valid minute is within the hour
        i = two_digit_values.index(minute)
        if i + 1 < len(two_digit_values) and two_digit_values[i + 1] < "60":
            return hour + ":" + two_digit_values[i + 1]

        # Check if the next valid hour is within the day
        i = two_digit_values.index(hour)
        if i + 1 < len(two_digit_values) and two_digit_values[i + 1] < "24":
            return two_digit_values[i + 1] + ":" + two_digit_values[0]

        # Return the earliest time of the next day
        return two_digit_values[0] + ":" + two_digit_values[0]