First Bad Version问题及解法

问题描述：

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.

问题分析：

采用二分查找，时间复杂度O(lg N)，这里有个编程细节：

在求mid中点值时，mid = left + (right - left) / 2比mid = (left + right) / 2运算速度要快。

过程详见代码：

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