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]

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. 

//那麼寫個二分查詢吧
public int firstBadVersion2(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;
}

git：https://github.com/woshiyexinjie/leetcode-xin