text: // All valid credit card numbers
  const valid1 = [4, 5, 3, 9, 6, 7, 7, 9, 0, 8, 0, 1, 6, 8, 0, 8];
  const valid2 = [5, 5, 3, 5, 7, 6, 6, 7, 6, 8, 7, 5, 1, 4, 3, 9];
  const valid3 = [3, 7, 1, 6, 1, 2, 0, 1, 9, 9, 8, 5, 2, 3, 6];
  const valid4 = [6, 0, 1, 1, 1, 4, 4, 3, 4, 0, 6, 8, 2, 9, 0, 5];
  const valid5 = [4, 5, 3, 9, 4, 0, 4, 9, 6, 7, 8, 6, 9, 6, 6, 6];
  
  // All invalid credit card numbers
  const invalid1 = [4, 5, 3, 2, 7, 7, 8, 7, 7, 1, 0, 9, 1, 7, 9, 5];
  const invalid2 = [5, 7, 9, 5, 5, 9, 3, 3, 9, 2, 1, 3, 4, 6, 4, 3];
  const invalid3 = [3, 7, 5, 7, 9, 6, 0, 8, 4, 4, 5, 9, 9, 1, 4];
  const invalid4 = [6, 0, 1, 1, 1, 2, 7, 9, 6, 1, 7, 7, 7, 9, 3, 5];
  const invalid5 = [5, 3, 8, 2, 0, 1, 9, 7, 7, 2, 8, 8, 3, 8, 5, 4];
  
  // Can be either valid or invalid
  const mystery1 = [3, 4, 4, 8, 0, 1, 9, 6, 8, 3, 0, 5, 4, 1, 4];
  const mystery2 = [5, 4, 6, 6, 1, 0, 0, 8, 6, 1, 6, 2, 0, 2, 3, 9];
  const mystery3 = [6, 0, 1, 1, 3, 7, 7, 0, 2, 0, 9, 6, 2, 6, 5, 6, 2, 0, 3];
  const mystery4 = [4, 9, 2, 9, 8, 7, 7, 1, 6, 9, 2, 1, 7, 0, 9, 3];
  const mystery5 = [4, 9, 1, 3, 5, 4, 0, 4, 6, 3, 0, 7, 2, 5, 2, 3];
  
  // An array of all the arrays above
  const batch = [
    valid1,
    valid2,
    valid3,
    valid4,
    valid5,
    invalid1,
    invalid2,
    invalid3,
    invalid4,
    invalid5,
    mystery1,
    mystery2,
    mystery3,
    mystery4,
    mystery5,
  ];
  
  // Add your functions below:
  
  const validateCred = (credNumber) => {
    let counter = 1;
    let credCheck = 0;
  
    for (let i = credNumber.length - 1; i >= 0; i--) {
      if (counter % 2 !== 0) {
        credCheck = credCheck + credNumber[i];
        //console.log('ungerade ' + counter + ' summe ' + credCheck);
      } else {
        credCheck = credCheck + credNumber[i] * 2;
        //console.log('gerade ' + counter + ' summe ' + credCheck);
        if (credNumber[i] * 2 > 9) {
          credCheck = credCheck - 9;
          //console.log('groesser als 9 Summe ' + credCheck);
        }
      }
      counter++;
    }
    if (credCheck % 10 === 0) {
      return true;
    } else {
      return false;
    }
  };
  
  const findInvalidCards = (cards) => {
    let invalidCards = [];
    cards.forEach((card) => {
      if (!validateCred(card)) {
        invalidCards.push(card);
      }
    });
    return invalidCards;
  };
  
  const idInvalidCardCompanies = (cardNumbers) => {
    let companysReturn = [];
  
    cardNumbers.forEach((cardNumber) => {
      switch (cardNumber[0]) {
        case 3:
          if (!companysReturn.find((element) => element === 'Amex')) {
            companysReturn.push('Amex');
          }
          break;
        case 4:
          if (!companysReturn.find((element) => element === 'Visa')) {
            companysReturn.push('Visa');
          }
          break;
        case 5:
          if (!companysReturn.find((element) => element === 'Mastercard')) {
            companysReturn.push('Mastercard');
          }
          break;
        case 6:
          if (!companysReturn.find((element) => element === 'Discover')) {
            companysReturn.push('Discover');
          }
          break;
        default:
          console.log('Company not found');
      }
    });
    return companysReturn;
  };
  
  let invalidCardsResult = findInvalidCards(batch);
  
  let invalidCardCompanys = idInvalidCardCompanies(invalidCardsResult);
  
  console.log(invalidCardCompanys);
  