Binary Watch

Binary Watch

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.

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”]

Solution

@高效的暴力搜索
class Solution(object):
    def readBinaryWatch(self, num):
        """
        :type num: int
        :rtype: List[str]
        """
        ret = []
        for i in range(12):
            for j in range(60):
                if bin(i).count('1')+bin(j).count('1')== num:
                    ret.append('%d:%02d'%(i,j))
        return ret

@DFS写法失败了 待研究 https://leetcode.com/problems/binary-watch/
class Solution(object):
    def readBinaryWatch(self, num):
        """
        :type num: int
        :rtype: List[str]
        """
        self.hour_list = [1,2,4,8,16,32]
        ret = []
        if num>=8:
            return ret
        for i in range(min(4,num+1)):
            self.generate(i, num-i, 0, 0, ret)
        return ret
        
    def generate(self, hour, minute, hour_value, minute_value, ret):
        if hour==0 and minute==0:
            if hour_value>=12 or minute_value>=60:
                return
            if minute_value<10:
                retstr = str(hour_value)+':0'+str(minute_value)
            else:
                retstr = str(hour_value)+':'+str(minute_value)
            if retstr in ret:
                return
            ret.append(retstr)
            return
        if hour>0:
            for i in range(4):
                self.generate(hour-1, minute, hour_value+self.hour_list[i], minute_value, ret)
        if minute>0:
            for i in range(6):
                self.generate(hour, minute-1, hour_value, minute_value+self.hour_list[i], ret)