LeetCode 0278 - First Bad Version

Given n = 5, and version = 4 is the first bad version.

call isBadVersion(3) -> false
call isBadVersion(5) -> true
call isBadVersion(4) -> true

Then 4 is the first bad version.

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

class Solution {
public:
    long long firstBadVersion(long long n) {
        long long left = 1;
        long long right = n;
        long long res = n;
        while(left <= right) {
            long long mid = (left + right) >> 1;
            if(isBadVersion(mid)) {
                res = mid;
                right = mid - 1;
            } else {
                left = mid + 1;
            }
        }
        return res;
    }
};