hellofresh.js

// cashMachine, returningAmount -> 5,5,5 | 10, 5

function calculate(customerBills) {
  const cashMachine = {
    5: 0,
    10: 0,
    20: 0
  };
  let totalCashInHand = 0;

  for (let index = 0; index < customerBills.length; index++) {
    const customerBill = customerBills[index];
    const returningAmount = customerBill - 5;

    if (returningAmount > totalCashInHand) {
      return false;
    }

    if (returningAmount === 5) {
      if (cashMachine[5] === 0) {
        return false;
      }
      cashMachine[5]--;
    }

    if (returningAmount === 15) {
      if (cashMachine[5] === 0 && cashMachine[10] === 0) {
        return false;
      }
      cashMachine[5]--;
      cashMachine[10]--;
    }

    totalCashInHand += 5;
    cashMachine[customerBill]++;
  }

  return true;
}

console.log('[5,10,5,20] -> true', calculate([5,10,5,20]))
console.log('[5, 20, 5, 20] -> false', calculate([5, 20, 5, 20]))
console.log('[5, 10, 5, 5, 5, 20, 10] -> true', calculate([5, 10, 5, 5, 5, 20, 10]))

console.log('[] -> false', calculate([]))
console.log('[5,10,10] -> false', calculate([5,10,10]))
console.log('[5,5,10,5] -> ', calculate([5,5,10,5]))
console.log('[10,5,5] -> ', calculate([10,5,5]))