[Leetcode + Lintcode] 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.

 

Binary Search解决，相当于finding the first appearance of bad version or last appearance of good version

java for leetcode, python for lincode

1. java

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

2. python

class Solution:
    """
    @param n: An integers.
    @return: An integer which is the first bad version.
    """
    def findFirstBadVersion(self, n):
        # write your code here
        start = 0
        while (start + 1 < n):
            mid = start + (n-start)/2
            if SVNRepo.isBadVersion(mid):
                n = mid
            else:
                start = mid
        
        if SVNRepo.isBadVersion(start):
            return start
        return n