下课了，做道简单题。

A binary watch has 4 LEDs on the top which represent the hours (0-11), and the 6 LEDs on the bottom represent the minutes (0-59).

Each LED represents a zero or one, with the least significant bit on the right.


For example, the above binary watch reads "3:25".

Given a non-negative integer n which represents the number of LEDs that are currently on, return all possible times the watch could represent.

Example:

Input: n = 1
Return: ["1:00", "2:00", "4:00", "8:00", "0:01", "0:02", "0:04", "0:08", "0:16", "0:32"]

Note:

  • The order of output does not matter.
  • The hour must not contain a leading zero, for example "01:00" is not valid, it should be "1:00".
  • The minute must be consist of two digits and may contain a leading zero, for example "10:2" is not valid, it should be "10:02". 

import itertools

class Solution(object):
    def getHour(self, n):
        '''
        n >=0 n<4
        '''
        if n==0:
            return [0]
        hours = []
        idxs = [0,1,2,3]
        temp = ['0','0','0','0']
        for change_idxs in itertools.combinations(idxs,n):
            for v in change_idxs:
                temp[v] = '1'
            
            value = int(''.join(temp),2)
            for v in change_idxs:
                temp[v] = '0'
            
            if value <= 11:
                hours.append(value)
        return hours
    
    def getMinutes(self, n):
        '''
        n>=0 n<=59
        '''
        if n==0:
            return [0]
        minutes = []
        idxs = [0,1,2,3,4,5]
        temp = ['0','0','0','0','0','0']
        for change_idxs in itertools.combinations(idxs,n):
            for v in change_idxs:
                temp[v] = '1'
            value = int(''.join(temp),2)
            for v in change_idxs:
                temp[v] = '0'
            if value <= 59:
                minutes.append(value)
        return minutes
        
        
        
    def readBinaryWatch(self, num):
        """
        :type num: int
        :rtype: List[str]
        """
        ans = []
        for h in range(4):
            m = num-h
            if m>=0:
                hours = self.getHour(h)
                minutes = self.getMinutes(m)
                for h_val, m_val in itertools.product(hours,minutes):
                    ans.append('{}:{:0>2d}'.format(h_val,m_val))
        return ans