LeetCode-Easy部分中标签为 Binary Search 278. First Bad Version

原题

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.

代码分析

二分查找应用到第一个坏版本查找上。

代码实现

最需要注意的是溢出！！！mid等要设置为long

        public int FirstBadVersion(int n)
        {
            long lo = 0; //指向好的版本
            long hi = n; //指向坏的版本
            long mid;
            while (hi - lo > 1)
            {
                mid = (lo + hi) >> 1; //写为这样就不怕溢出(lo + (hi-lo)/2)
                if (IsBadVersion(mid))
                    hi = mid;
                else 
                    lo = mid;
            }
            return (int)hi;
        }