LintCode First Bad Version

找出第一个出问题的version。

/**
 * public class SVNRepo {
 *     public static boolean isBadVersion(int k);
 * }
 * you can use SVNRepo.isBadVersion(k) to judge whether
 * the kth code version is bad or not.
*/
class Solution {
    /**
     * @param n: An integers.
     * @return: An integer which is the first bad version.
     */
    public int findFirstBadVersion(int n) {
        if(n <= 0) return -1;

        int left = 1; int right = n;
        while(left + 1 < right){
            int mid = (left + right) / 2;
            if(SVNRepo.isBadVersion(mid) == true){
                right = mid;
            }
            else{
                left = mid;
            }
        }
        if(SVNRepo.isBadVersion(left)){
            return left;
        }
        else if(SVNRepo.isBadVersion(right)){
            return right;
        }
        else return -1;
    }
}