LintCode (74) First Bad Version

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.

Have you met this question in a real interview? 

Yes

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.

Note

Please read the annotation in code area to get the correct way to call isBadVersion in different language. For example, Java isVersionControl.isBadVersion(v)

Challenge

You should call isBadVersion as few as possible.

说了一堆废话其实就是让你用binary search去找找。。。一看第一个xxx。。。果断上模板。。。lol

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/** * class VersionControl { * public: * static bool isBadVersion(int k); * } * you can use VersionControl::isBadVersion(k) to judge wether * the kth code version is bad or not. */ class Solution { public: /** * @param n: An integers. * @return: An integer which is the first bad version. */ int findFirstBadVersion(int n) { // write your code here if (n<=0) return 0; int beg=1; int end=n; while(beg+1<end){ int mid=beg+(end-beg)/2; if (VersionControl::isBadVersion(mid)) end=mid; else beg=mid; } if (VersionControl::isBadVersion(beg)) return beg; if (VersionControl::isBadVersion(end)) return end; return 0; } };