firstBadVersion.java

// 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.

/* The isBadVersion API is defined in the parent class VersionControl.
      boolean isBadVersion(int version); */

public class Solution extends VersionControl {

    public int firstBadVersion(int n) {
        
        int start = 1;
        int end = n;
        
        while(start < end) {
            
            int mid = start + (end - start) / 2;
            if(!isBadVersion(mid)) start = mid + 1;
            else end = mid;
            
        }
        
        return start;
        
    }

}