leetcode 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.
这题按理说是很简单的，二分查找嘛。单提交答案却出现wrong answer，还是负的，不可能啊。试了几次都出现这样的情况，百思不得其解。想了好久，突然想到一处可能出现错误，high+low可能出现溢出，操，改了之后就通过了。

bool isBadVersion(int version);

int firstBadVersion(int n) {
if (isBadVersion(1))
return 1;
long long int low = 1,high = n;
while (high > low)
{
if (isBadVersion(high))
{
long long int r=(high + low) / 2;
high = r;
}
else
{
long long int r=2 * high - low;
if(r>n)
high=n;
else
high=r;
r= (low + high) / 2;;
low =r;
}
}
return high+1;
}

accepted