[leetcode]: 278. First Bad Version

1.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.
假设你是一个产品经理，团队开发了一个产品的一系列版本（共n个），但由于中途某个版本k有问题，导致这个版本k之后的所有版本都有问题。
目标：找出这个K，提供isBadVersion API用于判断版本i是否有问题。

2.分析

二分查找

3.代码

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