# Fetch Items To Display
###### tags: `Implementation`, `Amazon OA`

Description:
Amazon website contains one to many items in each page. To mimic the logic of the website, an Amazon programmer has a list of items and each item has its name, relevance and price. After sorting the items by `[name:0, relevance:1, price:2]`, the programmer is trying to find out a list of items displayed in a chosen page.

Given a list of items, the `sort parameter`, the `sort order = (0: ascending, 1:descending)`, the number of items to be displayed in each page and a page number, write an algorithm to *determine the list of item names in the specified page while respecting the item's order*. Page Number starts from 0.

* **Example**

numOfItems = 3
items: ["item1",10,15],["item2",3,4],["item3",17,8]
sortParameter: 1
sortOrder: 0
itemsPerPage: 2
pageNumber: 1

Output:
{"item3"}

Solution:

public class WebsiteItemSorting {
    class DisplayItem {
        String name;
        int relevance;
        int price;
        public DisplayItem(String name, int relevance, int price) {
            this.name = name;
            this.relevance = relevance;
            this.price = price;
        }
    }

    public List<String> WebsiteItemSorting(int numOfItems, Map<String, int[]> items, int sortParameter,
                                           int sortOrder, int itemPerPage, int pageNumber)
    {
        List<DisplayItem> list = new ArrayList<>();
        for (String key : items.keySet()) {
            int[] info = items.get(key);
            list.add(new DisplayItem(key, info[0], info[1]));
        }
        Collections.sort(list, getComp(sortOrder, sortParameter));

        List<String> res = new ArrayList<>();
        for (int i = pageNumber * itemPerPage; i < pageNumber * (itemPerPage + 1) && i < numOfItems; i++) {
            res.add(list.get(i).name);
        }
        return res;
    }

    private Comparator<DisplayItem> getComp(int sortOrder, int sortParameter) {
        Comparator<DisplayItem> comparator = new Comparator<DisplayItem>() {
            @Override
            public int compare(DisplayItem o1, DisplayItem o2) {
                int res = 0;
                switch (sortParameter) {
                    case 0:
                        res = o1.name.compareTo(o2.name);
                        break;
                    case 1:
                        res = o1.relevance - o2.relevance;
                        break;
                    case 2:
                        res = o1.price - o2.price;
                        break;
                }
                return sortOrder == 1 ? -res : res;
            }
        };
        return comparator;
    }
}