[LeetCode] First Bad Version

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

class Solution {
public:
int firstBadVersion(int n) {
int l = 1, r = n;
while (l < r) {
int m = l + (r - l) / 2;
if (isBadVersion(m)) r = m;
else l = m + 1;
}
return l;
}
};