[LeetCode] Challenge log 401

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401. Binary Watch

https://leetcode.com/problems/binary-watch/description/

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:

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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”.
Solution:
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# cache all (number of leds, mins/hours} in dict
# check all combination 
class Solution:
    def readBinaryWatch(self, num):
        """
        :type num: int
        :rtype: List[str]
        """
        hours = {}
        for i in range(12):
            numberOfLed = bin(i).count('1')
            if numberOfLed not in hours:
                hours[numberOfLed] = [str(i)]
            else:
                hours[numberOfLed].append(str(i))
        print(hours)     
        mins = {}
        for i in range(60):
            if i >= 10: 
                temp = str(i) 
            else:
                temp = '0' + str(i)
            numberOfLed = bin(i).count('1')
            if numberOfLed not in mins:
                mins[numberOfLed] = [temp]
            else:
                mins[numberOfLed].append(temp)
        print(mins)
        
        results = []
        for h in range(num+1):
            m = num - h
            if m in mins and h in hours:
                results = results + [ hh + ':' + mm for hh in hours[h] for mm in mins[m]]
                
        return results
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# same idea but 200% neater
class Solution:
    def readBinaryWatch(self, num):
        """
        :type num: int
        :rtype: List[str]
        """
        return ["{}:{:0>2d}".format(i,j) for i in range(12) for j in range(60) \
                if bin(i).count('1') + bin(j).count('1') == num]
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