Solving the problem of allocating amounts for multiple orders and multiple payment methods in Java

It is considered an interview question. The description of the problem is as follows: Multiple business orders correspond to one payment order, and a combined payment is used during payment. Then how to calculate the payment method and amount assigned to each order.

A total of three payment method combinations A, B, and C account for 100, 100, and 80 respectively.

There are two orders in total. 1 order amount is 80, and 2 order amount is 200.

After allocation, 4 orders and data with different payment methods are generated.

Draw a picture to make it clearer:

Abstract of the problem:

We found that Figure 1 and Figure 2 overlapped and soon after, Figure 3 Assign the results.

But the code doesn’t seem to be that simple to operate.

I have materialized the problem again. The payment method combination can be imagined as different types of cups, and the order combination is different types of wine. Now I want to put the wine into my life. Each countdown counts data for a combination of order and payment method.

The first time: Wine No. 1 started to arrive, but it was not even full in cup A, so it was all poured out. The data is 1+A+80

The second time: Pour No. 2 wine into A and the remaining 20 rain is full. The data is 2+A+20

The third time: Pour No. 2 wine into cup B, fill it with 100, and there is still 80 of No. 2 wine. The data is 2+B+100

The fourth time: Wine No. 2 was poured into cup C, and it was almost empty. The data is 2+C+80

We found that these four operations are to traverse the data of the order combination and occupy the data of the remaining payment amount in turn. And times 2, 3, and 4 are an iterative code process.

If you happen to have time, you can implement it yourself using the code you are familiar with. By the way, I will also collect various implementation methods and ideas.

So one implementation is as follows:

public class ItemDistribution {

    private List<Entry> cupList = new ArrayList<>();

    /**
     * 初始化
     * @param list
     */
    public ItemDistribution(List<Item> list) {
        if(list == null || list.size()<=0){
            return;
        }
        Integer start = 0;
        Integer end = 0;
        for(Item item : list){
            end = start + item.amount;
            Entry entry = new Entry(start, end, item.payMethod);
            start = end;
            cupList.add(entry);
        }
    }

    /**
     * 分配
     * @param orderIdAmountMap
     * @return
     */
    public List<Item> getOrderInfoItemList(Map<Integer, Integer> orderIdAmountMap){
        if(cupList == null){
            return null;
        }
        List<Entry> cupTransferList = cupList;
        List<Item> returnItems = new ArrayList<>();
        for (Map.Entry<Integer, Integer> orderIdAmountEntry : orderIdAmountMap.entrySet()) {
            Integer orderId = orderIdAmountEntry.getKey();
            Integer orderAmount = orderIdAmountEntry.getValue();
            buildItem(orderId, orderAmount, cupTransferList, returnItems);
        }
        return returnItems;
    }

    /**
     * 单个cup分配
     * @param orderId
     * @param orderAmount
     * @param cupList
     * @param returnItems
     */
    private void buildItem(Integer orderId, Integer orderAmount, List<Entry> cupList, List<Item> returnItems) {
        if(IntegerUtil.isZero(orderAmount) || orderId == null){
            return;
        }

        Entry cup = getLatestCup(cupList);
        if(cup == null){
            return;
        }
        Integer remain = cup.end - cup.index;
        Item item = null;
        if(remain > orderAmount){
            cup.index = cup.start + orderAmount;
            item = new Item(orderId, orderAmount, cup.payMethod);
            returnItems.add(item);
            return;
        }else{
            cup.index = cup.end;
            item = new Item(orderId, remain, cup.payMethod);
            returnItems.add(item);
            orderAmount = orderAmount - remain;
        }

        buildItem(orderId, orderAmount, cupList, returnItems);
    }

    /**
     * 获得可用的cup
     * @param cupTransferList
     * @return
     */
    private Entry getLatestCup(List<Entry> cupTransferList){
        for(Entry cup : cupTransferList){
            if(!IntegerUtil.isEquals(cup.index, cup.end)){
                return cup;
            }
        }
        return null;
    }

    public class Entry{
        private Integer start;
        private Integer end;
        private Integer index = 0;
        private Integer payMethod;

        public Entry(Integer start, Integer end, Integer payMethod) {
            this.start = start;
            this.index = start;
            this.end = end;
            this.payMethod = payMethod;
        }
    }


    public static void main(String[] args) {
        List<Item> list = new ArrayList<Item>();
        Item OrderPayInfoItem1 = new Item(100,1);
        Item OrderPayInfoItem2 = new Item(100,2);
        Item OrderPayInfoItem3 = new Item(80,3);
        list.add(OrderPayInfoItem1);
        list.add(OrderPayInfoItem2);
        list.add(OrderPayInfoItem3);
        ItemDistribution itemDistribution = new ItemDistribution(list);

        Map map = new HashMap<>();
        map.put(1001, 80);
        map.put(1002, 200);
        List<Item> returnList = itemDistribution.getOrderInfoItemList(map);
    }
}

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