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😡 LeetCode 278. First Bad Version

  • Date : 2021.06.20(일)
  • Time : 20분

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. 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.

Constraints

  • 1 <= n <= 2&31 - 1
  • 1 <= pick <= n

Example

  • 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.



풀이

    def firstBadVersion(self, n):
        mi, ni = 1, n

        while mi < ni:
            mid = (mi + ni) // 2
            if isBadVersion(mid):
                ni = mid
            else:
                mi = mid + 1

        return mi

: 이전에 풀었던 문제들처럼 Binary Search의 문제이다. 일단 이 문제는 isBadVersion이라는 api가 기본으로 제공된다. 이 api를 이용해 현재 api에 넣은 버전이 오류 버전인지 아닌지 판단해서 값을 올려주고 내려주는 문제이다.