LeetCode-278-First Bad Version-E（寻找第一个次品）

最新推荐文章于 2020-07-31 11:07:04 发布

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#数据结构与算法

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本文介绍了一种使用二分查找算法来高效确定首次出现故障产品版本的方法。在一个由多个连续开发的软件版本中，一旦某个版本开始出现故障，其后续的所有版本也将受到影响。通过调用一个预设的API isBadVersion(version)，可以判断任意版本是否为故障版本。文章提供了一个实现示例，展示了如何在最少的API调用次数下找到首个故障版本。

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.

思路：二分查找，找到序列中的第一个不合格的产品，代码如下（isBadVersion是题中已给函数）

bool isBadVersion(int version);
 
int firstBadVersion(int n) {
        int low=1,high=n;
        while(low<=high){
            int mid=low + (high-low)/2;
            if(isBadVersion(mid))
                high=mid-1;
            else
                low=mid+1;
        }
        return low;
    }