swmansion_algorithmic_task

/**
 * after 6 every prime number will be form of 6n-1 and 6n+1
 * @param element
 */
function isPrime(element) {
  if (element < 6) {
    if (element < 2) {
      return false;
    }
    return element !== 4;
  }
  return (element + 1) % 6 === 0 || (element - 1) % 6 === 0
}

function countFrequencies(items) {
  return items.reduce((accum, number) => {
    if (!accum[number]) {
      accum[number] = 0;
    }
    accum[number]++;
    return accum;
  }, {});
}

function output(A, B) {
  const freq = countFrequencies(B);
  return A.reduce((accum, number) => {
    if (isPrime(freq[number])) {
      return accum;
    }
    return [...accum, number]
  }, [])
}

/**
 * time complexity is O(A + B)
 */