Introduction

In this blog post, we will explore how to solve the LeetCode problem "278" 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

You are a product manager and currently leading a team to develop a new product. Unfortunately, the latest version of your product fails the quality check. Since each version is developed based on the previous version, all the versions after a bad version are also bad. Suppose you have n versions [1, 2, ..., n] and you want to find out the first bad one, which causes all the following ones to be bad. You are given an API bool isBadVersion(version) which returns whether version is bad. Implement a function to find the first bad version. You should minimize the number of calls to the API. Example 1: Input: n = 5, bad = 4 Output: 4 Explanation: call isBadVersion(3) -> false call isBadVersion(5) -> true call isBadVersion(4) -> true Then 4 is the first bad version. Example 2: Input: n = 1, bad = 1 Output: 1 Constraints: 1 <= bad <= n <= 231 - 1

Explanation

Here's the solution to find the first bad version:

• Binary Search: The core idea is to use binary search to efficiently narrow down the range of possible bad versions. Since versions after a bad version are also bad, we can exploit this sorted-like property to quickly eliminate half of the search space in each iteration.

• Minimize API Calls: Binary search minimizes the calls to isBadVersion() by strategically probing the middle element of the current search space. This logarithmic approach ensures we find the first bad version with the fewest possible queries.

• Runtime Complexity: O(log n) & Storage Complexity: O(1)

Code

    def firstBadVersion(n: int) -> int:
    """
    You are a product manager and currently leading a team to develop a new product.
    Unfortunately, the latest version of your product fails the quality check.
    Since each version is developed based on the previous version, all the versions after a bad version are also bad.
    Suppose you have n versions [1, 2, ..., n] and you want to find out the first bad one, which causes all the following ones to be bad.
    You are given an API bool isBadVersion(version) which returns whether version is bad.
    Implement a function to find the first bad version. You should minimize the number of calls to the API.

    Example 1:
    Input: n = 5, bad = 4
    Output: 4
    Explanation:
    call isBadVersion(3) -> false
    call isBadVersion(5) -> true
    call isBadVersion(4) -> true
    Then 4 is the first bad version.

    Example 2:
    Input: n = 1, bad = 1
    Output: 1

    Constraints:
    1 <= bad <= n <= 231 - 1
    """

    left, right = 1, n

    while left < right:
        mid = left + (right - left) // 2  # Prevent potential overflow
        if isBadVersion(mid):
            right = mid  # First bad version could be 'mid' or earlier
        else:
            left = mid + 1  # First bad version is later than 'mid'

    return left  # 'left' will eventually point to the first bad version


# Dummy isBadVersion function for testing (replace with actual API call)
def isBadVersion(version: int) -> bool:
    bad = 4 # Example bad version for testing
    return version >= bad