Design a simplified version of Twitter where users can post tweets, follow/unfollow another user and is able to see the 10 most recent tweets in the user's news feed. Your design should support the following methods:
- postTweet(userId, tweetId): Compose a new tweet.
- getNewsFeed(userId): 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.
- follow(followerId, followeeId): Follower follows a followee.
- unfollow(followerId, followeeId): Follower unfollows a followee.
Example:
Twitter twitter = new Twitter(); // User 1 posts a new tweet (id = 5). twitter.postTweet(1, 5); // User 1's news feed should return a list with 1 tweet id -> [5]. twitter.getNewsFeed(1); // User 1 follows user 2. twitter.follow(1, 2); // User 2 posts a new tweet (id = 6). twitter.postTweet(2, 6); // User 1's news feed should return a list with 2 tweet ids -> [6, 5]. // Tweet id 6 should precede tweet id 5 because it is posted after tweet id 5. twitter.getNewsFeed(1); // User 1 unfollows user 2. twitter.unfollow(1, 2); // User 1's news feed should return a list with 1 tweet id -> [5], // since user 1 is no longer following user 2. twitter.getNewsFeed(1);
系统设计题，设计一个简单的推特，有发布消息，获得新鲜事，添加关注和取消关注等功能。
参考：linspiration
Java:
public class Twitter {
Map<Integer, Set<Integer>> userMap = new HashMap<>();
Map<Integer, LinkedList<Tweet>> tweets = new HashMap<>();
int timestamp = 0;
class Tweet {
int time;
int id;
Tweet(int time, int id) {
this.time = time;
this.id = id;
}
}
public void postTweet(int userId, int tweetId) {
if (!userMap.containsKey(userId)) userMap.put(userId, new HashSet<>());
userMap.get(userId).add(userId);
if (!tweets.containsKey(userId)) tweets.put(userId, new LinkedList<>());
tweets.get(userId).addFirst(new Tweet(timestamp++, tweetId));
}
public List<Integer> getNewsFeed(int userId) {
if (!userMap.containsKey(userId)) return new LinkedList<>();
PriorityQueue<Tweet> feed = new PriorityQueue<>((t1, t2) -> t2.time-t1.time);
userMap.get(userId).stream().filter(f -> tweets.containsKey(f))
.forEach(f -> tweets.get(f).forEach(feed::add));
List<Integer> res = new LinkedList<>();
while (feed.size() > 0 && res.size() < 10) res.add(feed.poll().id);
return res;
}
public void follow(int followerId, int followeeId) {
if (!userMap.containsKey(followerId)) userMap.put(followerId, new HashSet<>());
userMap.get(followerId).add(followeeId);
}
public void unfollow(int followerId, int followeeId) {
if (userMap.containsKey(followerId) && followeeId != followerId) userMap.get(followerId).remove(followeeId);
}
}
Python:
class Twitter(object):
def __init__(self):
"""
Initialize your data structure here.
"""
self.__number_of_most_recent_tweets = 10
self.__followings = collections.defaultdict(set)
self.__messages = collections.defaultdict(list)
self.__time = 0
def postTweet(self, userId, tweetId):
"""
Compose a new tweet.
:type userId: int
:type tweetId: int
:rtype: void
"""
self.__time += 1
self.__messages[userId].append((self.__time, tweetId))
def getNewsFeed(self, userId):
"""
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.
:type userId: int
:rtype: List[int]
"""
max_heap = []
if self.__messages[userId]:
heapq.heappush(max_heap, (-self.__messages[userId][-1][0], userId, 0))
for uid in self.__followings[userId]:
if self.__messages[uid]:
heapq.heappush(max_heap, (-self.__messages[uid][-1][0], uid, 0))
result = []
while max_heap and len(result) < self.__number_of_most_recent_tweets:
t, uid, curr = heapq.heappop(max_heap)
nxt = curr + 1;
if nxt != len(self.__messages[uid]):
heapq.heappush(max_heap, (-self.__messages[uid][-(nxt+1)][0], uid, nxt))
result.append(self.__messages[uid][-(curr+1)][1]);
return result
def follow(self, followerId, followeeId):
"""
Follower follows a followee. If the operation is invalid, it should be a no-op.
:type followerId: int
:type followeeId: int
:rtype: void
"""
if followerId != followeeId:
self.__followings[followerId].add(followeeId)
def unfollow(self, followerId, followeeId):
"""
Follower unfollows a followee. If the operation is invalid, it should be a no-op.
:type followerId: int
:type followeeId: int
:rtype: void
"""
self.__followings[followerId].discard(followeeId)
C++:
class Twitter {
public:
/** Initialize your data structure here. */
Twitter() : time_(0) {
}
/** Compose a new tweet. */
void postTweet(int userId, int tweetId) {
messages_[userId].emplace_back(make_pair(++time_, tweetId));
}
/** 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. */
vector<int> getNewsFeed(int userId) {
using RIT = deque<pair<size_t, int>>::reverse_iterator;
priority_queue<tuple<size_t, RIT, RIT>> heap;
if (messages_[userId].size()) {
heap.emplace(make_tuple(messages_[userId].rbegin()->first,
messages_[userId].rbegin(),
messages_[userId].rend()));
}
for (const auto& id : followings_[userId]) {
if (messages_[id].size()) {
heap.emplace(make_tuple(messages_[id].rbegin()->first,
messages_[id].rbegin(),
messages_[id].rend()));
}
}
vector<int> res;
while (!heap.empty() && res.size() < number_of_most_recent_tweets_) {
const auto& top = heap.top();
size_t t;
RIT begin, end;
tie(t, begin, end) = top;
heap.pop();
auto next = begin + 1;
if (next != end) {
heap.emplace(make_tuple(next->first, next, end));
}
res.emplace_back(begin->second);
}
return res;
}
/** Follower follows a followee. If the operation is invalid, it should be a no-op. */
void follow(int followerId, int followeeId) {
if (followerId != followeeId && !followings_[followerId].count(followeeId)) {
followings_[followerId].emplace(followeeId);
}
}
/** Follower unfollows a followee. If the operation is invalid, it should be a no-op. */
void unfollow(int followerId, int followeeId) {
if (followings_[followerId].count(followeeId)) {
followings_[followerId].erase(followeeId);
}
}
private:
const size_t number_of_most_recent_tweets_ = 10;
unordered_map<int, unordered_set<int>> followings_;
unordered_map<int, deque<pair<size_t, int>>> messages_;
size_t time_;
};
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