leetcode First Bad Version题解

最新推荐文章于 2024-11-06 09:58:18 发布

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本文介绍了一个产品版本控制问题，即如何使用最少的函数调用找到首个出现故障的版本。通过二分查找法，我们可以在大量版本中高效定位问题源头。

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 versionis 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.

中文理解：一个产品有一系列的版本号，从1-n，其中一个版本i有问题，则i-n均有问题，使用最少的isBadVersion函数调用找出i 版本号。

解题思路：显然使用二分查找法。

代码（java）：

祝：把mid=（start+end）/2就会超时，很诡异。。。。

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

public class Solution extends VersionControl {
    public int firstBadVersion(int n) {
        //使用二分查找的方法
        int start=1;
        int end=n;
        while(start<end){
            int mid = start + (end-start) / 2;
            if(isBadVersion(mid))end=mid;
            else start=mid+1;
        }
        return isBadVersion(start)? start:start+1;
    }
}