Java [Leetcode 278]First Bad Version

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 version is bad. Implement a function to find the first bad version. You should minimize the number of calls to the API.

解题思路：

使用二分法查找。同时注意二分法查找时候中间位置的数值不能溢出。

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