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