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.

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.

思路：

• 题意：给定1～n个数字代表产品，其中一个产品坏了，后面的全坏，要求检测第一个坏的（提供了函数）
• 二分法，这里的二分法判断条件比较特殊，当然后面的设置变量要用long，没想明白

代码：

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

public class Solution extends VersionControl {
    public int firstBadVersion(int n) {
         long begin = 1;
        long end = n;
        if(n<1) return 0;
        while(begin<end){
            long mid = (begin+end)/2;
            if(isBadVersion((int)mid)){
                end = mid-1;
            }else{
                begin = mid+1;
            }
        }
        if(isBadVersion((int)begin)) return (int)begin;
        return (int)begin+1;
    }
}