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