solution.py

class Solution(object):
    def readBinaryWatch(self, num):
        """
        :type num: int
        :rtype: List[str]
        """
        pre_hours_map = {
            0: ['0'],
            1: ['1', '2', '4', '8'],
            2: ['3', '5', '9', '6', '10'],
            3: ['7', '11']
        }
        pre_mins_map = {
            0: ['00'],
            1: ['01', '02', '04', '08', '16', '32'],
            2: ['03', '05', '09', '17', '33', '06', '10', '18', '34', '12', '20', '36', '24', '40', '48'],
            3: ['07', '11', '19', '35', '13', '21', '37', '25', '41', '49', '14', '22', '38', '26', '42', '50', '28', '44', '52', '56'],
            4: ['15', '23', '39', '27', '43', '51', '29', '45', '53', '57', '30', '46', '54', '58'],
            5: ['31', '47', '55', '59']
        }
        
        res = []
        
        for i in range(4):
            if pre_mins_map.get(num - i):
                for x in pre_hours_map.get(i):
                    for y in pre_mins_map.get(num - i):
                        res.append(x + ':' + y)
        return res