//1 2 3 ...... k-1 k k+1 .... n 
//0 0 0         0  X  X  .... X
/**
 * class SVNRepo {
 *     public:
 *     static bool isBadVersion(int k);
 * }
 * you can use SVNRepo::isBadVersion(k) to judge whether 
 * 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
        int start = 1;
        int end = n;

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