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 havenVersions[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 APIbool isBadVersion(version)Which will return whetherversionIs bad. Implement a function to find the first bad version. You shoshould Minimize the number of cballs to the API.

Example:

Given n = 5, and version = 4 is the first bad version.call isBadVersion(3) -> falsecall isBadVersion(5) -> truecall isBadVersion(4) -> trueThen 4 is the first bad version. 

 

Approach #1:

// Forward declaration of isBadVersion API.bool isBadVersion(int version);class Solution {public:    int firstBadVersion(int n) {        int l = 1;        int r = n;        int m;        while (l <= r) {            m = l + (r - l) / 2;            if (isBadVersion(m)) r = m - 1;            else l = m + 1;        }        return l;    }};

Runtime: 0 MS, faster than 100.00% of C ++ online submissions for first bad version.

 

Analysis:

1. Using

 

278. First bad version