LeetCode BinarySearch 278 first bad version

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本文介绍了一种高效查找软件中第一个引入错误的版本的方法，通过使用二分搜索策略，最小化了调用质量检查API的次数，从而快速定位问题源头。

Leetcode 278 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.

Example:

Given n = 5, and version = 4 is the first bad version.

call isBadVersion(3) -> false
call isBadVersion(5) -> true
call isBadVersion(4) -> true

Then 4 is the first bad version.

public class Solution extends VersionControl {
    public int firstBadVersion(int n) {
        if (n == 1) return 1; 
        int lo = 0;
        int hi = n;
        
        while (lo + 1 < hi) {
            int mid = lo + (hi - lo) / 2;
            if (isBadVersion(mid)) {
                hi = mid;
            } else {
                lo = mid;
            }
        }
        
        return isBadVersion(lo) ? lo:hi;
    }
}