function beautifulPairs(A, B) {
  let mp = {};
  let result = 0;

  for (let i = 0; i < A.length; i++) {
    mp[A[i]] = (mp[A[i]] || 0) + 1;
  }

  for (let i = 0; i < B.length; i++) {
    if (mp[B[i]] > 0) {
      mp[B[i]]--;
      result++;
    }
  }
  const isEmpty = Object.keys(mp).every(key => mp[key] === 0);

  return result === A.length ? (isEmpty ? result : result - 1) : result + 1;
}

console.log(beautifulPairs([1, 2, 3, 4], [1, 2, 4, 3]));