lintcode-medium-First Bad 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) {
        // write your code here
        
        if(n <= 1)
            return 1;
        
        int left = 1;
        int right = n;
        
        while(left < right){
            int mid = left + (right - left) / 2;
            
            if(SVNRepo.isBadVersion(mid))
                right = mid;
            else
                left = mid + 1;
        }
        
        return left;
    }
}