278. First Bad Version

最新推荐文章于 2020-10-26 10:49:14 发布

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最新推荐文章于 2020-10-26 10:49:14 发布

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分类专栏： LeetCode Binary Search 文章标签： Binary Search Leetcode First Bad Version

本文链接：https://blog.youkuaiyun.com/zshouyi/article/details/54579900

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本文介绍了一种使用二分搜索算法来高效找出导致后续版本皆为故障版本的第一个故障版本的方法。给定一系列版本号，通过调用isBadVersion()API判断版本好坏，并以此找到故障起始点。

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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.

Credits:
Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.

寻找第一个坏的版本，即寻找最后一个好的版本，返回lb+1，属于寻找lowerbound。参考模板：模板：Binary Search - 二分搜索。这里选择lb=0，up=n。代码如下：

/* The isBadVersion API is defined in the parent class VersionControl.
      boolean isBadVersion(int version); */

public class Solution extends VersionControl {
    public int firstBadVersion(int n) {
        int lb = 0, ub = n;
        while (lb + 1 < ub) {
            int mid = lb + (ub - lb) / 2;
            if (!isBadVersion(mid)) {
                lb = mid;
            } else {
                ub = mid;
            }
        }
        return lb + 1;
    }
}