Introduction

In this blog post, we will explore how to solve the LeetCode problem "401" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

Problem Statement

A binary watch has 4 LEDs on the top to represent the hours (0-11), and 6 LEDs on the bottom to represent the minutes (0-59). Each LED represents a zero or one, with the least significant bit on the right. For example, the below binary watch reads "4:51". Given an integer turnedOn which represents the number of LEDs that are currently on (ignoring the PM), return all possible times the watch could represent. You may return the answer in any order. The hour must not contain a leading zero. For example, "01:00" is not valid. It should be "1:00". The minute must consist of two digits and may contain a leading zero. For example, "10:2" is not valid. It should be "10:02". Example 1: Input: turnedOn = 1 Output: ["0:01","0:02","0:04","0:08","0:16","0:32","1:00","2:00","4:00","8:00"] Example 2: Input: turnedOn = 9 Output: [] Constraints: 0 <= turnedOn <= 10

Explanation

Here's the breakdown of the problem and the solution:

• Core Idea: Iterate through all possible hour (0-11) and minute (0-59) combinations. For each combination, calculate the total number of set bits (1s) in the binary representation of the hour and minute. If the sum of set bits equals the given turnedOn value, add the formatted time to the result.
• Bit Counting: Use the bin(n).count('1') method for an efficient way to count set bits in an integer.

• Formatting: Ensure that the hour is represented without leading zeros (as an integer), and the minute is formatted with leading zeros if necessary (using {:02d} format specifier).

• Time and Space Complexity: O(1) time complexity since the loops iterate a constant number of times, and O(1) space complexity as the output list's maximum size is bounded.

Code

    def readBinaryWatch(turnedOn: int) -> list[str]:
    """
    Given the number of turned on LEDs, returns all possible times the binary watch could represent.
    """
    result = []
    for hour in range(12):
        for minute in range(60):
            if bin(hour).count('1') + bin(minute).count('1') == turnedOn:
                result.append(f"{hour}:{minute:02d}")
    return result