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‎src/main/java/com/fishercoder/solutions/_355.java

+229-97
Original file line numberDiff line numberDiff line change
@@ -22,152 +22,284 @@
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Twitter twitter = new Twitter();
2424
25-
// User 1 posts a new tweet (id = 5).
25+
// User 1 posts a new tweet (userId = 5).
2626
twitter.postTweet(1, 5);
2727
28-
// User 1's news feed should return a list with 1 tweet id -> [5].
28+
// User 1's news feed should return a list with 1 tweet userId -> [5].
2929
twitter.getNewsFeed(1);
3030
3131
// User 1 follows user 2.
3232
twitter.follow(1, 2);
3333
34-
// User 2 posts a new tweet (id = 6).
34+
// User 2 posts a new tweet (userId = 6).
3535
twitter.postTweet(2, 6);
3636
3737
// User 1's news feed should return a list with 2 tweet ids -> [6, 5].
38-
// Tweet id 6 should precede tweet id 5 because it is posted after tweet id 5.
38+
// Tweet userId 6 should precede tweet userId 5 because it is posted after tweet userId 5.
3939
twitter.getNewsFeed(1);
4040
4141
// User 1 unfollows user 2.
4242
twitter.unfollow(1, 2);
4343
44-
// User 1's news feed should return a list with 1 tweet id -> [5],
44+
// User 1's news feed should return a list with 1 tweet userId -> [5],
4545
// since user 1 is no longer following user 2.
4646
twitter.getNewsFeed(1);
4747
*/
4848
public class _355 {
49-
//credit: https://discuss.leetcode.com/topic/48100/java-oo-design-with-most-efficient-function-getnewsfeed
50-
public static class Twitter {
5149

52-
private static int timestamp = 0;
53-
private Map<Integer, User> map;
50+
public static class Solution1 {
51+
/**
52+
* reference: https://discuss.leetcode.com/topic/48100/java-oo-design-with-most-efficient-function-getnewsfeed
53+
*/
54+
public static class Twitter {
5455

55-
class Tweet {
56-
public int time;
57-
public int id;
58-
public Tweet next;//have a pointer, so we could be more memory efficient when retrieving tweets, think about merging k sorted lists
56+
private static int timestamp = 0;
57+
private Map<Integer, User> map;
5958

60-
public Tweet(int id) {
61-
this.id = id;
62-
time = timestamp++;
63-
next = null;
59+
class Tweet {
60+
public int time;
61+
public int id;
62+
public Tweet next;
63+
/**have a pointer,
64+
* so we could be more memory efficient when retrieving tweets,
65+
* think about merging k sorted lists*/
66+
67+
public Tweet(int id) {
68+
this.id = id;
69+
time = timestamp++;
70+
next = null;
71+
}
6472
}
65-
}
6673

67-
//the meat part of this OO design, have a User object itself, have follow() and unfollow() method embedded inside it
68-
class User {
69-
public int id;
70-
public Set<Integer> followed;
71-
public Tweet tweetHead;
72-
73-
public User(int id) {
74-
this.id = id;
75-
followed = new HashSet<>();
76-
followed.add(id);//followe itself first
77-
this.tweetHead = null;
74+
/**
75+
* the meat part of this OO design problem,
76+
* have a User object itself,
77+
* have follow() and unfollow() method embedded inside it
78+
*/
79+
class User {
80+
public int id;
81+
public Set<Integer> followed;
82+
public Tweet tweetHead;
83+
84+
public User(int id) {
85+
this.id = id;
86+
followed = new HashSet<>();
87+
followed.add(id);//follow oneself first
88+
this.tweetHead = null;
89+
}
90+
91+
public void follow(int followeeId) {
92+
followed.add(followeeId);
93+
}
94+
95+
public void unfollow(int followeeId) {
96+
followed.remove(followeeId);
97+
}
98+
99+
public void postTweet(int tweetId) {
100+
//every time we post, we prepend it to the head of the tweet
101+
Tweet head = new Tweet(tweetId);
102+
head.next = tweetHead;
103+
tweetHead = head;//don't forget to overwrite tweetHead with the new head
104+
}
78105
}
79106

80-
public void follow(int followeeId) {
81-
followed.add(followeeId);
107+
/**
108+
* Initialize your data structure here.
109+
*/
110+
public Twitter() {
111+
map = new HashMap();
82112
}
83113

84-
public void unfollow(int followeeId) {
85-
followed.remove(followeeId);
114+
/**
115+
* Compose a new tweet.
116+
*/
117+
public void postTweet(int userId, int tweetId) {
118+
/**update oneself newsFeed first and also all of his followers' newsFeed*/
119+
if (!map.containsKey(userId)) {
120+
User user = new User(userId);
121+
map.put(userId, user);
122+
}
123+
map.get(userId).postTweet(tweetId);
86124
}
87125

88-
public void postTweet(int tweetId) {
89-
//every time we post, we prepend it to the head of the tweet
90-
Tweet head = new Tweet(tweetId);
91-
head.next = tweetHead;
92-
tweetHead = head;//don't forget to overwrite tweetHead with the new head
126+
/**
127+
* Retrieve the 10 most recent tweet ids in the user's news feed. Each item in the news feed must be posted by users who the user followed or by the user herself. Tweets must be ordered from most recent to least recent.
128+
*/
129+
public List<Integer> getNewsFeed(int userId) {
130+
List<Integer> newsFeed = new LinkedList<>();
131+
if (!map.containsKey(userId)) {
132+
return newsFeed;
133+
}
134+
Set<Integer> users = map.get(userId).followed;
135+
PriorityQueue<Tweet> heap = new PriorityQueue<>(users.size(), (a, b) -> b.time - a.time);
136+
for (int user : users) {
137+
Tweet tweet = map.get(user).tweetHead;
138+
//it's super important to check null before putting into the heap
139+
if (tweet != null) {
140+
heap.offer(tweet);
141+
}
142+
}
143+
144+
int count = 0;
145+
while (!heap.isEmpty() && count < 10) {
146+
Tweet tweet = heap.poll();
147+
newsFeed.add(tweet.id);
148+
count++;
149+
if (tweet.next != null) {
150+
heap.offer(tweet.next);
151+
}
152+
}
153+
154+
return newsFeed;
93155
}
94-
}
95156

96-
/** Initialize your data structure here. */
97-
public Twitter() {
98-
map = new HashMap();
99-
}
157+
/**
158+
* Follower follows a followee. If the operation is invalid, it should be a no-op.
159+
*/
160+
public void follow(int followerId, int followeeId) {
161+
if (!map.containsKey(followeeId)) {
162+
User user = new User(followeeId);
163+
map.put(followeeId, user);
164+
}
100165

101-
/** Compose a new tweet. */
102-
public void postTweet(int userId, int tweetId) {
103-
//update oneself newsFeed and also all of his followers' newsFeed
104-
if (!map.containsKey(userId)) {
105-
User user = new User(userId);
106-
map.put(userId, user);
166+
if (!map.containsKey(followerId)) {
167+
User user = new User(followerId);
168+
map.put(followerId, user);
169+
}
170+
171+
map.get(followerId).follow(followeeId);
107172
}
108-
User user = map.get(userId);
109-
user.postTweet(tweetId);
110-
}
111173

112-
/** Retrieve the 10 most recent tweet ids in the user's news feed. Each item in the news feed must be posted by users who the user followed or by the user herself. Tweets must be ordered from most recent to least recent. */
113-
public List<Integer> getNewsFeed(int userId) {
114-
List<Integer> newsFeed = new LinkedList<>();
115-
if (!map.containsKey(userId)) {
116-
return newsFeed;
174+
/**
175+
* Follower unfollows a followee. If the operation is invalid, it should be a no-op.
176+
*/
177+
public void unfollow(int followerId, int followeeId) {
178+
if (!map.containsKey(followerId) || followeeId == followerId) {
179+
return;
180+
}
181+
map.get(followerId).unfollow(followeeId);
117182
}
118-
Set<Integer> users = map.get(userId).followed;
119-
PriorityQueue<Tweet> heap = new PriorityQueue<>(users.size(), (a, b) -> b.time - a.time);
120-
for (int user : users) {
121-
Tweet tweet = map.get(user).tweetHead;
122-
//it's super important to check null before putting into the heap
123-
if (tweet != null) {
124-
heap.offer(tweet);
183+
/**
184+
* Your Twitter object will be instantiated and called as such:
185+
* Twitter obj = new Twitter();
186+
* obj.postTweet(userId,tweetId);
187+
* List<Integer> param_2 = obj.getNewsFeed(userId);
188+
* obj.follow(followerId,followeeId);
189+
* obj.unfollow(followerId,followeeId);
190+
*/
191+
}
192+
}
193+
194+
public static class Solution2 {
195+
public static class Twitter {
196+
197+
Map<Integer, User> map;
198+
private int timestamp;
199+
200+
private class User {
201+
private int userId;
202+
private Set<Integer> followed;
203+
private Tweet tweetHead;
204+
205+
public User(int userId) {
206+
this.userId = userId;
207+
this.followed = new HashSet<>();
208+
this.followed.add(userId);
209+
this.tweetHead = null;
210+
}
211+
212+
public void postTweet(int tweetId) {
213+
Tweet tweet = new Tweet(tweetId);
214+
tweet.next = tweetHead;
215+
tweetHead = tweet;
216+
}
217+
218+
public void follow(int followeeId) {
219+
followed.add(followeeId);
220+
}
221+
222+
public void unfollow(int followeeId) {
223+
followed.remove(followeeId);
125224
}
225+
126226
}
127227

128-
int count = 0;
129-
while (!heap.isEmpty() && count < 10) {
130-
Tweet tweet = heap.poll();
131-
newsFeed.add(tweet.id);
132-
count++;
133-
if (tweet.next != null) {
134-
heap.offer(tweet.next);
228+
private class Tweet {
229+
int time;
230+
int id;
231+
Tweet next;
232+
233+
public Tweet(int id) {
234+
this.id = id;
235+
time = timestamp++;
236+
next = null;
135237
}
136238
}
137239

138-
return newsFeed;
139-
}
240+
/** Initialize your data structure here. */
241+
public Twitter() {
242+
map = new HashMap<>();
243+
timestamp = 0;
244+
}
140245

141-
/** Follower follows a followee. If the operation is invalid, it should be a no-op. */
142-
public void follow(int followerId, int followeeId) {
143-
if (!map.containsKey(followeeId)) {
144-
User user = new User(followeeId);
145-
map.put(followeeId, user);
246+
/** Compose a new tweet. */
247+
public void postTweet(int userId, int tweetId) {
248+
if (!map.containsKey(userId)) {
249+
User user = new User(userId);
250+
map.put(userId, user);
251+
}
252+
map.get(userId).postTweet(tweetId);
146253
}
147254

148-
if (!map.containsKey(followerId)) {
149-
User user = new User(followerId);
150-
map.put(followerId, user);
255+
/** Retrieve the 10 most recent tweet ids in the user's news feed. Each item in the news feed must be posted by users who the user followed or by the user herself. Tweets must be ordered from most recent to least recent. */
256+
public List<Integer> getNewsFeed(int userId) {
257+
List<Integer> result = new LinkedList<>();
258+
if (!map.containsKey(userId)) {
259+
return result;
260+
}
261+
Set<Integer> followeeSet = map.get(userId).followed;
262+
PriorityQueue<Tweet> maxHeap = new PriorityQueue<>((a, b) -> b.time - a.time);
263+
for (int followeeId : followeeSet) {
264+
if (map.containsKey(followeeId)) {
265+
Tweet tweet = map.get(followeeId).tweetHead;
266+
if (tweet != null) {
267+
maxHeap.offer(tweet);
268+
}
269+
}
270+
}
271+
272+
int count = 0;
273+
while (!maxHeap.isEmpty() && count++ < 10) {
274+
Tweet tweet = maxHeap.poll();
275+
if (tweet != null) {
276+
result.add(tweet.id);
277+
if (tweet.next != null) {
278+
maxHeap.offer(tweet.next);
279+
}
280+
}
281+
}
282+
return result;
151283
}
152284

153-
map.get(followerId).follow(followeeId);
154-
}
285+
/** Follower follows a followee. If the operation is invalid, it should be a no-op. */
286+
public void follow(int followerId, int followeeId) {
287+
if (!map.containsKey(followerId)) {
288+
map.put(followerId, new User(followerId));
289+
}
290+
if (!map.containsKey(followeeId)) {
291+
map.put(followeeId, new User(followeeId));
292+
}
293+
map.get(followerId).follow(followeeId);
294+
}
155295

156-
/** Follower unfollows a followee. If the operation is invalid, it should be a no-op. */
157-
public void unfollow(int followerId, int followeeId) {
158-
if (!map.containsKey(followerId) || followeeId == followerId) {
159-
return;
296+
/** Follower unfollows a followee. If the operation is invalid, it should be a no-op. */
297+
public void unfollow(int followerId, int followeeId) {
298+
if (!map.containsKey(followerId) || followeeId == followerId) {
299+
return;
300+
}
301+
map.get(followerId).unfollow(followeeId);
160302
}
161-
map.get(followerId).unfollow(followeeId);
162303
}
163304
}
164-
165-
/**
166-
* Your Twitter object will be instantiated and called as such:
167-
* Twitter obj = new Twitter();
168-
* obj.postTweet(userId,tweetId);
169-
* List<Integer> param_2 = obj.getNewsFeed(userId);
170-
* obj.follow(followerId,followeeId);
171-
* obj.unfollow(followerId,followeeId);
172-
*/
173305
}

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