278. First Bad Version

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：二分搜索，加上题目的一些理解。注意二分搜索的算mid的时候不能写成(end+start)/2, 虽然意义上是对的，但是如果end和start都很大的时候相加会溢出。

// Forward declaration of isBadVersion API.bool isBadVersion(int version);class Solution {public:    int firstBadVersion(int n) {        int start = 1, end = n;        while(start < end)        {            int mid = start + (end - start)/2;            if(isBadVersion(mid))            {                end = mid -1;            }            else            {                start = mid + 1;            }        }       if(isBadVersion(start))       {           return start;       }       else       {           return start+1;       }    }};