// Forward declaration of isBadVersion API.bool isBadVersion(int version);class Solution {public:    int firstBadVersion(int n) {        int left=1;        int right=n;        while(left<=right){            int mid=left+(right-left)/2;            if(isBadVersion(mid))  right=mid-1;            else  left=mid+1;        }        return left;    }};