EASY 0278. First Bad Version

Problem Statement

Leetcode Link

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.

Examples

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.

Constraints

1 <= bad <= n <= 231 - 1

Solution

This is similar to a binary search.

Solution
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"""Solution for the Leetcode problem #0278 First Bad Version
https://leetcode.com/problems/first-bad-version/

"""


def isBadVersion(version) -> bool:
    import random
    return random.choice([True, False])


def first_bad_version(n):
    """Given a function whose calls are to be limited, identify the first bad version"""
    start = 1
    end = n
    last_bad = None
    while start <= end:
        mid_point = (start + end) // 2
        if isBadVersion(mid_point):
            last_bad = mid_point
            end = mid_point - 1
        else:
            start = mid_point + 1

    return last_bad