function arrayDifference(firstArray: number[], secondArray: number[]): number[] {
  const leftNumbersMap = new Map<number, boolean>()
   firstArray.forEach(leftValue =>{
      leftNumbersMap.set(leftValue, true);
  });

  secondArray.forEach(rightValue =>{
    const mapEntry = leftNumbersMap.get(rightValue);
    if(!!mapEntry){
      leftNumbersMap.set(rightValue, false)
    }
  }

  )

  return leftNumbersMap.entries().toArray().filter(keyValue => keyValue[1] === true).map(keyValue => keyValue[0])
}

// No modificar: necesario para evaluar el resultado.
export { arrayDifference };