LeetCode278 First Bad Version

文章目录
  1. 1. 描述
  2. 2. 样例
  3. 3. 思路
  4. 4. 代码

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.

样例

1

思路

在$n$个版本的产品中,找出第一个坏版本。

有一个性质是,坏版本之后的版本都是坏版本。使用普通的二分搜索即可,如果当前版本是坏版本,那么减少上界,否则增加下界。

代码

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// Forward declaration of isBadVersion API.
bool isBadVersion(int version);

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