First Bad Version

题目：

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.

Example: Given n = 5:

isBadVersion(3) -> false

isBadVersion(5) -> true

isBadVersion(4) -> true

分析：

题目本身难度不高，但是记得在call判断的时候用

SVNRepo::isBadVersion(k) instead of isBadVersion(k)

解法：

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 false;
        }
        if (n ==1) {
            return SVNRepo::isBadVersion(1);
        }
        int start = 1;
        int end = n;
        while (start + 1 < end) {
            int mid = start + (end - start) / 2;
            if (SVNRepo::isBadVersion(mid) ) {
                end = mid;
            } else {
                start = mid;
            }
        }

        if (SVNRepo::isBadVersion(start) ) {
            return start;
        }
        if (SVNRepo::isBadVersion(end) ) {
            return end;
        }
        return -1;
    }
};