leetcode之first bad version

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.

解答：

很明显的binary search注意和普通二分查找的区别，同时注意在求mid的时候尽量写成l + (r - l) / 2的形式，防止溢出// Forward declaration of isBadVersion API.
bool isBadVersion(int version);

class Solution {
public:
int firstBadVersion(int n) {
int l = 1;
int r = n;
while(l < r)
{
int mid = l + (r - l)/2;
if(isBadVersion(mid))
r = mid;
else
l = mid + 1;
}
return l;
}
};