PaginateListings.java

class PaginateListings {

    static class Listing {
        Float score;
        String hostId;
        String listing;
        Listing(float s, String h, String l) {
            score = s;
            hostId = h;
            listing = l;
        }
    }

    static class Host {
        String hostId;
        LinkedList<Listing> listings = new LinkedList<>();
        Host(String s) {
            hostId = s;
        }
    }

    static Listing getListingFromString(String s) {
        String[] fields = s.split(",");
        String hostId = fields[0];
        float score = Float.parseFloat(fields[2]);
        return new Listing(score,hostId,s);
    }

    static List<String> getSortedPages(ArrayList<String> listings, int perPage) {
        Set<String> set = new HashSet<>();
        PriorityQueue<Host> duplicates = new PriorityQueue<>((a,b)->b.listings.getFirst().score.compareTo(a.listings.getFirst().score));
        Map<String,Host> map = new HashMap<>();
        List<String> output = new ArrayList<>();

        int count = 0;
        for(int i=1; i<listings.size(); i++) {
            if(count > 0 && count % perPage == 0) {
                set.clear();
                count = 0;
                LinkedList<Host> temp = new LinkedList<>();
                while(!duplicates.isEmpty()) {
                    Host h = duplicates.poll();
                    output.add(h.listings.removeFirst().listing);
                    set.add(h.hostId);
                    temp.add(h);
                    count++;
                }
                while(!temp.isEmpty()) {
                    Host h = temp.removeFirst();
                    if(h.listings.size() > 0) {
                        duplicates.add(h);
                    }
                }         
            }
            Listing l = getListingFromString(listings.get(i));
            if(!set.contains(l.hostId)) {
                output.add(l.listing);
                set.add(l.hostId);
                count++;
            } else {
                Host h = map.computeIfAbsent(l.hostId, k->new Host(l.hostId));
                h.listings.add(l);
                if(h.listings.size() == 1) { // Not in priority queue
                    duplicates.add(h);
                }
            }
        }
        while(!duplicates.isEmpty()) {
            Host h = duplicates.poll();
            output.add(h.listings.removeFirst().listing);
            if(h.listings.size() > 0) {
                duplicates.add(h);
            }
        }
        return output;
    }
}