278. First Bad Version

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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.

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. 

 1 // Forward declaration of isBadVersion API. 2 //二分尋找 3 bool isBadVersion(int version); 4 /*如果w??hile語句在left == right時運行，它會進入無限迴圈，因為它始終是if（isBadVersion（mid））{right = mid; }。因此，要退出while語句，它應該保持<right，以便在它= = right時退出。*/ 5 int firstBadVersion(int n) { 6     int left=1,right=n; 7     while (left < right) { 8         int mid = left + (right - left) / 2; 9         if (isBadVersion(mid)) {10             right = mid;11         } else {12             left = mid + 1;13         }14     }15     return left;16 }

 

278. First Bad Version