First Bad Version 二分查找

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.

public class Solution extends VersionControl {


    public int firstBadVersion(int n) {

        int start=1;

        int end=n;

        int mid;

        while(start<=end){

            mid=((end-start)>>1)+start;//二分查找，这种写法不错

            //mid=(start+end)/2;//这样会溢出，所以选择写成上边那样，妙不妙

            if(isBadVersion(mid))

                end=mid-1;//注意

            else

                start=mid+1;//注意

        }

       //return end+1;//注意

       return start;//这俩都可以，因为最后循环结束时，一定有start>end且只大1

    }

}