First Bad Version

// Forward declaration of isBadVersion API.
bool isBadVersion(int version);

class Solution {
public:
    int firstBadVersion(int n) {
        int left = 1 , right = n;

        while(left + 1 < right){
            int mid = left + (right - left)/2;

            if(isBadVersion(mid)){
                right = mid;
            }
            else{
                left = mid;
            }
        }

        if(isBadVersion(left)) return left;

        if(isBadVersion(right)) return right;
    }
};