Suppose you have n versions with the IDs [1,2,...,n], and you have access to an API function that returns TRUE if the argument is the ID of a bad version. Your task is to find the first bad version, which is causing all the later ones to be bad. You have to implement a solution with the minimum number of API calls.

find-first-bad-version.js

export function firstBadVersion(n) {
  // -- DO NOT CHANGE THIS SECTION
  versionApi.n = n;
  // --

  let start = 1;
  let end = n;
  let count = 0;

  while (start < end) {
    let mid = Math.floor((start + end) / 2);
    count += 1;
    if (isBadVersion(mid)) {
      // we dont do end = mid - 1 here because
      // if mid is actually the first bad version,
      // doing -1 will shift us to the left of it,
      // and we will never return back to it
      end = mid;
    } else {
      start = mid + 1;
    }
  }

  return [start, count];
}