183.First Bad Version

题目：

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.

您是产品经理，目前领导团队开发新产品。 不幸的是，您产品的最新版本未通过质量检查。 由于每个版本都是基于以前的版本开发的，因此糟糕版本之后的所有版本也都很糟糕。

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.

假设您有n个版本[1,2，...，n]并且您想找出第一个坏的版本，这会导致以下所有版本都不好。

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.

您将获得一个API bool isBadVersion（版本），它将返回版本是否错误。 实现一个函数来查找第一个坏版本。 您应该最小化对API的调用次数。

Example:

Given n = 5, and version = 4 is the first bad version.
给定n = 5，版本= 4是第一个坏版本。

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

Then 4 is the first bad version. 

解答：

/* 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 left=1,right=n;
        while(left<right){
            int mid=left+(right-left)/2;
            if(isBadVersion(mid)) right=mid;
            else left=mid+1;
        }
        return left;
    }
}

详解：

显然二分查找法