LeetCode #278 - First Bad Version

最新推荐文章于 2023-10-30 10:53:14 发布

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本文介绍了一种使用二分查找算法来高效定位软件中首次出现的坏版本的方法。在一个由1到n版本组成的列表中，一旦某个版本出现问题，则该版本及其后续所有版本都将受到影响。通过调用API isBadVersion(version)，可以判断指定版本是否为坏版本，并最终找出首个出现问题的版本。

题目描述：

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 will return whether version is bad. Implement a function to find the first bad version. You should minimize the number of calls to the API.

Example:

Given n = 5, and version = 4 is the first bad version.

call isBadVersion(3) -> false
call isBadVersion(5) -> true
call isBadVersion(4) -> true

Then 4 is the first bad version.

提供一个API能够确定某个版本号是否为坏版本，对弈一个版本号，如果它是坏版本，那么它之后的所有版本都是坏版本，找到第一个坏版本。为了降低时间复杂度，考虑采用二分法，如果mid不是坏版本，那么搜索范围为前半段，否则坏版本为mid或者位于后半段，所以分情况讨论即可。

class Solution {
public:
    int firstBadVersion(int n) {
        int begin=1;
        int end=n;
        while(begin<=end)
        {
            int mid=begin+(end-begin)/2;
            if(isBadVersion(mid))
            {
                if(mid==begin||!isBadVersion(mid-1)) return mid;
                else end=mid-1;
            }
            else begin=mid+1;
        }
    }
};