What is the main approach to solving the Binary Watch problem?

The main approach involves using backtracking with pruning and bit manipulation to efficiently generate all valid times with the specified number of LEDs turned on.

How does bit manipulation help in solving this problem?

Bit manipulation allows you to efficiently represent the watch time, count the set bits (turned-on LEDs), and directly check for valid hour and minute combinations.

What are common mistakes when solving the Binary Watch problem?

Common mistakes include failing to handle edge cases, like impossible configurations, and not properly managing the leading zeros in the hour component.

How do we handle edge cases in the Binary Watch problem?

Edge cases, like when turnedOn is too large for a valid time, are handled by pruning the search space and skipping invalid combinations early in the backtracking process.

How can GhostInterview assist with the Binary Watch problem?

GhostInterview assists by providing solutions to optimize the backtracking process, using bit manipulation for efficient counting, and helping with common pitfalls like handling edge cases.

#401

Easy

auto_awesome回溯·pruning

LeetCode 题解工作台

二进制手表

二进制手表顶部有 4 个 LED 代表小时（0-11），底部的 6 个 LED 代表分钟（0-59）。每个 LED 代表一个 0 或 1，最低位在右侧。例如，下面的二进制手表读取 "4:51" 。给你一个整数 turnedOn ，表示当前亮着的 LED 的数量，返回二进制手表可以表示的所…

回溯位运算

题目描述

二进制手表顶部有 4 个 LED 代表 小时（0-11），底部的 6 个 LED 代表 分钟（0-59）。每个 LED 代表一个 0 或 1，最低位在右侧。

例如，下面的二进制手表读取 "4:51" 。

给你一个整数 turnedOn ，表示当前亮着的 LED 的数量，返回二进制手表可以表示的所有可能时间。你可以 按任意顺序 返回答案。

小时不会以零开头：

例如，"01:00" 是无效的时间，正确的写法应该是 "1:00" 。

分钟必须由两位数组成，可能会以零开头：

例如，"10:2" 是无效的时间，正确的写法应该是 "10:02" 。

示例 1：

输入：turnedOn = 1
输出：["0:01","0:02","0:04","0:08","0:16","0:32","1:00","2:00","4:00","8:00"]

示例 2：

输入：turnedOn = 9
输出：[]

提示：

0 <= turnedOn <= 10

lightbulb

解题思路

方法一：枚举组合

题目可以转换为求 $i \in [0, 12)$ 和 $j \in [0, 60)$ 的所有可能组合。

合法组合需要满足的条件是 $i$ 的二进制形式中 1 的个数加上 $j$ 的二进制形式中 1 的个数，结果等于 $\textit{turnedOn}$ 。

时间复杂度 $O(1)$ ，空间复杂度 $O(1)$ 。

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class Solution:
    def readBinaryWatch(self, turnedOn: int) -> List[str]:
        return [
            '{:d}:{:02d}'.format(i, j)
            for i in range(12)
            for j in range(60)
            if (bin(i) + bin(j)).count('1') == turnedOn
        ]

speed

复杂度分析

指标	值
时间	Depends on the final approach
空间	Depends on the final approach

psychology

面试官常问的追问

外企场景

question_mark
Look for an understanding of backtracking and how it can be applied to the problem.
question_mark
Check for familiarity with bit manipulation and its role in efficiently solving problems with binary representations.
question_mark
Ensure the candidate is aware of edge cases, such as when turnedOn is 9 (impossible configuration).

warning

常见陷阱

外企场景

error
Failing to handle edge cases like impossible configurations where turnedOn is too large to form a valid time.
error
Not properly handling leading zeros in the hour component.
error
Overcomplicating the solution by not utilizing bit manipulation and pruning effectively, leading to inefficiency.

swap_horiz

进阶变体

外企场景

arrow_right_alt
Consider optimizing the solution for different input ranges, such as turnedOn being larger than 10.
arrow_right_alt
Modify the problem to generate only times that are specific to a given hour or minute range.
arrow_right_alt
Adapt the problem to include time intervals or add additional constraints, such as ensuring the time is within a certain range.

help

常见问题

外企场景

继续练习

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