LeetCode-278.First Bad Version

https://leetcode.com/problems/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.

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

但是这里存在一个问题

如果mid的赋值使用mid=(l+r)/2，是不能通过的。

原因在于l+r可能导致溢出

因此

二分法的使用要注意mid因使用mid = l + (r - l) / 2;