1+ import java .io .BufferedReader ;
2+ import java .io .InputStreamReader ;
3+ import java .net .HttpURLConnection ;
4+ import java .net .URL ;
5+ import java .util .PriorityQueue ;
6+ import java .util .List ;
7+ import java .util .LinkedList ;
8+ import java .util .UUID ;
9+ 10+ import com .google .gson .Gson ;
11+ 12+ /*
13+ * GET API: https://jsonmock.hackerrank.com/api/food_outlets?page={page_no}
14+ */
15+ 16+ public class RestWithGson {
17+ final String BASE_URL = "https://jsonmock.hackerrank.com" ;
18+ final int TIMEOUT_MILLISEC = (int )1e3 ; // 1 sec timeout
19+ 20+ PriorityQueue <Hotel > getTopHotels (int top ){
21+ PriorityQueue <Hotel > topHotels = new PriorityQueue <Hotel >();
22+ // MAX Bounded Queue of Size `top`
23+ int currentPage = 0 ;
24+ int maxPages = 1 ;
25+ // todo: currently flow is sequential one by one page
26+ // we can spawn new thread pool of size K to get data to reduce overall network time
27+ // to MAX_PAGES/K
28+ while (currentPage < maxPages ){
29+ HotelPage currentSetOfHotels = getCurrentPage (currentPage );
30+ maxPages = currentSetOfHotels .totalPages ;
31+ if (currentSetOfHotels .data != null && currentSetOfHotels .data .size () == 0 ){
32+ System .out .println ("empty data\n " ); //todo: retry to get current page with exponential backoff
33+ break ;
34+ }
35+ add (currentSetOfHotels .data , topHotels , top );
36+ currentPage ++;
37+ }
38+ return topHotels ;
39+ }
40+ 41+ // make a network get call to get the current page data
42+ // and add it to queue as rolling window
43+ HotelPage getCurrentPage (int page ){
44+ String route = BASE_URL + "/api/food_outlets?page=" + page ;
45+ try {
46+ URL url = new URL (route );
47+ HttpURLConnection connection = (HttpURLConnection )url .openConnection ();
48+ connection .setRequestMethod ("GET" ); // anyway default it get but specifying it improves
49+ // code readibility
50+ connection .setConnectTimeout (TIMEOUT_MILLISEC );
51+ if (connection .getResponseCode () == 200 ){
52+ BufferedReader response = new BufferedReader (new InputStreamReader (connection .getInputStream ()));
53+ StringBuilder responseBuilder = new StringBuilder ();
54+ String line = null ;
55+ while ((line = response .readLine ()) != null ){
56+ responseBuilder .append (line );
57+ }
58+ return parseStringToCities (responseBuilder .toString ());
59+ }
60+ } catch (Exception exception ){
61+ System .out .println (exception );
62+ return null ;
63+ }
64+ return null ;
65+ }
66+ 67+ // deserialize text to object
68+ HotelPage parseStringToCities (String responseText ){
69+ // using gson to cast into
70+ Gson deserializer = new Gson ();
71+ return deserializer .fromJson (responseText , HotelPage .class );
72+ }
73+ 74+ // adding to bounded queue
75+ // add time: O(log `top`), space: O(top)
76+ void add (List <Hotel > currentSetOfHotels , PriorityQueue <Hotel > topHotels , int top ) {
77+ for (Hotel hotel : currentSetOfHotels ){
78+ // to ensure heap having at least `top` elements
79+ if (topHotels .size () < top ){
80+ topHotels .add (hotel );
81+ continue ;
82+ }
83+ // re-balancing heap in log n
84+ topHotels .add (hotel );
85+ topHotels .poll (); // todo: we can maintain maxHeap instad of minHeap
86+ // and we can check top element in O(1) and avoid everytime rebalancing heap
87+ // although it does not impact time complexity but a very good perf improvement
88+ }
89+ }
90+ 91+ void run ()throws Exception {
92+ PriorityQueue <Hotel > topHotels = getTopHotels (10 );
93+ while (!topHotels .isEmpty ()) {
94+ System .out .println ("top hotel:" + topHotels .poll ());
95+ }
96+ }
97+ 98+ public static void main (String [] args ) throws Exception {
99+ RestWithGson driver = new RestWithGson ();
100+ driver .run ();
101+ driver .closeResources ();
102+ }
103+ 104+ private void closeResources (){
105+ System .out .flush ();
106+ // clear up class level resources like io, dbconnections etc.
107+ }
108+ }
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