atm-easy.js

// Дан массив банкнот определенных номиналов
//     [1, 2, 5, 10, 20, 50],
//     их количество не ограничено.
//     Нужно выдать ему эти деньги используя минимальное количество купюр.

// reduceRight simple
const getCash1 = (bills, total) => {
    let totalRemain = total;

    return bills.reduceRight((acc, bill) => {
        const billCount = Math.floor(totalRemain / bill);

        if (billCount > 0 && totalRemain > 0) {
            totalRemain = totalRemain - billCount * bill;
            const billsToAdd = Array.from({length: billCount}, () => bill);
            acc.push(...billsToAdd);
        }
        return acc;
    }, []);
};

// sort + forEach simple
const getCash2 = (bills, total) => {
    const result = [];
    const sorted = bills.sort((a, b) => b - a);

    let totalRemain = total;
    sorted.forEach((bill) => {
        const billCount = Math.floor(totalRemain / bill);
        if (billCount > 0 && totalRemain > 0) {
            totalRemain = totalRemain - billCount * bill;
            const billsToAdd = Array.from({length: billCount}, () => bill);
            result.push(...billsToAdd);
        }
    });
    return result;
};

//  with additional checks
const getCash = (bills, total) => {
    let totalRemain = total;
    const fullExchangeBills = []
    const result = bills.sort((a, b) => b - a).reduce((acc, bill, idx) => {
        const billCount = Math.floor(totalRemain / bill)
        const canExchangeTotal = Number.isInteger(total / bill)
        if (canExchangeTotal) {
            fullExchangeBills.push([bill, total / bill])
        }
        if (billCount > 0 && totalRemain > 0) {
            totalRemain = totalRemain - billCount * bill;
            const billsToAdd = Array(billCount).fill(bill)
            acc.push(...billsToAdd);
        }
        // если на последней итерации остался остаток, значит нельзя выдать по простому алгоритму
        // выдать одинаковыми купюрами
        if (idx === bills.length - 1 && totalRemain > 0) {
            const fullExchangeBill = fullExchangeBills?.[0]?.[0]
            if (!fullExchangeBill) {
                return acc
            }
            const fullBillCount = fullExchangeBills[0][1]
            const fullBills = Array(fullBillCount).fill(Number(fullExchangeBill))
            totalRemain = 0
            return fullBills
        }
        return acc;
    }, [])

    if (totalRemain > 0) {
        return 'cant change'
    }
    return result
};

console.log(getCash([1, 2, 5, 10, 20, 50], 91)); // [ 50, 20, 20, 1 ]
console.log(getCash([1, 2, 5, 10, 20, 50], 82)); // [ 50, 20, 10, 2 ]
console.log(getCash([1, 2, 5, 10, 20, 50], 73)); // [ 50, 20, 2, 1 ]
console.log(getCash([1, 2, 5, 10, 20, 50], 40)); // [ 20, 20 ]
console.log(getCash([1, 2, 5, 10, 20, 50], 12)); // [ 10, 2 ]
console.log(getCash([1, 2, 5, 10, 20, 50], 3)); // [ 2, 1 ]
console.log(getCash([1, 2, 5, 10, 20, 50], 1)); // [ 1 ]
// additional
console.log(getCash([2, 3, 5, 50], 91)); // can't
console.log(getCash([200, 500], 600)); // [200,200,200]