First Bad Version.java

/*
The code base version is an integer start from 1 to n. One day, someone committed a bad version in the code case, 
so it caused this version and the following versions are all failed in the unit tests. Find the first bad version.

You can call isBadVersion to help you determine which version is the first bad one. 
The details interface can be found in the code's annotation part.

Example
Given n = 5:
isBadVersion(3) -> false
isBadVersion(5) -> true
isBadVersion(4) -> true
Here we are 100% sure that the 4th version is the first bad version.

time = O(logn)
space = O(1)
*/


// LintCode version
/**
 * public class SVNRepo {
 *     public static boolean isBadVersion(int k);
 * }
 * you can use SVNRepo.isBadVersion(k) to judge whether 
 * the kth code version is bad or not.
*/

public class Solution {
    public int findFirstBadVersion(int n) {
        // first occurance
        // time = O(logn), space = O(1)
        
        int left = 1;
        int right = n;
        while (left + 1 < right) {
            int mid = left + (right - left) / 2;
            if (SVNRepo.isBadVersion(mid)) {
                right = mid;
            } else {
                left = mid;
            }
        }
        
        return SVNRepo.isBadVersion(left) ? left : right;
    }
}


// LeetCode version
/* 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 left = 1;
        int right = n;
        while (left + 1 < right) {
            int mid = left + (right - left) / 2;
            if (isBadVersion(mid)) {
                right = mid;
            } else {
                left = mid;
            }
        }
        if (isBadVersion(left)) {
            return left;
        } else {
            return right;
        }
    }
}