First Bad Version — LeetCode 278 Python Solution

The problem

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.

Example

Input

n = 5, bad = 4

Output

4

Explanation

call isBadVersion(3) -> false

Python solution

# The isBadVersion API is already defined for you.
# def isBadVersion(version: int) -> bool:


class Solution:
    def firstBadVersion(self, n: int) -> int:
        l, r = 1, n
        while l < r:
            mid = (l + r) >> 1
            if isBadVersion(mid):
                r = mid
            else:
                l = mid + 1
        return l

Complexity

Pattern: Monotonic Stack

Answer "what is the next greater element" for every position in one pass. LeetCode 278. First Bad Version is filed here because the reference solution below belongs to the algorithm family this hub collects, even though its LeetCode tags point elsewhere.

The monotonic stack guide has the Python template for the pattern and the 225 LeetCode problems that use it.

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