design-twitter.py

"""

355. Design Twitter
Medium

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.

Implement the Twitter class:

Twitter() Initializes your twitter object.
void postTweet(int userId, int tweetId) Composes a new tweet with ID tweetId by the user userId. Each call to this function will be made with a unique tweetId.
List<Integer> getNewsFeed(int userId) Retrieves 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 themself. Tweets must be ordered from most recent to least recent.
void follow(int followerId, int followeeId) The user with ID followerId started following the user with ID followeeId.
void unfollow(int followerId, int followeeId) The user with ID followerId started unfollowing the user with ID followeeId.
 

Example 1:

Input
["Twitter", "postTweet", "getNewsFeed", "follow", "postTweet", "getNewsFeed", "unfollow", "getNewsFeed"]
[[], [1, 5], [1], [1, 2], [2, 6], [1], [1, 2], [1]]
Output
[null, null, [5], null, null, [6, 5], null, [5]]

Explanation
Twitter twitter = new Twitter();
twitter.postTweet(1, 5); // User 1 posts a new tweet (id = 5).
twitter.getNewsFeed(1);  // User 1's news feed should return a list with 1 tweet id -> [5]. return [5]
twitter.follow(1, 2);    // User 1 follows user 2.
twitter.postTweet(2, 6); // User 2 posts a new tweet (id = 6).
twitter.getNewsFeed(1);  // 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.unfollow(1, 2);  // User 1 unfollows user 2.
twitter.getNewsFeed(1);  // User 1's news feed should return a list with 1 tweet id -> [5], since user 1 is no longer following user 2.
 

Constraints:

1 <= userId, followerId, followeeId <= 500
0 <= tweetId <= 104
All the tweets have unique IDs.
At most 3 * 104 calls will be made to postTweet, getNewsFeed, follow, and unfollow.

"""


# V0
# https://github.com/labuladong/fucking-algorithm/blob/master/%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84%E7%B3%BB%E5%88%97/%E8%AE%BE%E8%AE%A1Twitter.md
from collections import defaultdict
from heapq import merge
class Twitter(object):
    
    def __init__(self):
        self.follower_followees_map = defaultdict(set)
        self.user_tweets_map = defaultdict(list)
        self.time_stamp = 0

    def postTweet(self, userId, tweetId):
        self.user_tweets_map[userId].append((self.time_stamp, tweetId))
        self.time_stamp -= 1

    def getNewsFeed(self, userId):
        # get the followees list
        followees = self.follower_followees_map[userId]
        # add userId as well, since he/she can also see his/her post in the timeline
        followees.add(userId)
        
        # reversed(.) returns a listreverseiterator, so the complexity is O(1) not O(n)
        candidate_tweets = [reversed(self.user_tweets_map[u]) for u in followees]

        tweets = []
        """
        python starred expression :

        -> will extend Iterable Unpacking

        example 1 : *candidate_tweets
        exmaple 2 : a, *b, c = range(5)

        ref :

        https://www.python.org/dev/peps/pep-3132/
        https://blog.csdn.net/weixin_41521681/article/details/103528136
        http://swaywang.blogspot.com/2012/01/pythonstarred-expression.html
        https://github.com/yennanliu/CS_basics/blob/master/doc/cheatsheet/python_trick.md
        """
        # complexity is 10*log(n), n is twitter's user number in worst case
        # both of below work
        candidates = list(merge(*candidate_tweets))
        #for t in merge(*candidate_tweets):
        for t in candidates:
            tweets.append(t[1])
            if len(tweets) == 10:
                break
        return tweets

    def follow(self, followerId, followeeId):
        self.follower_followees_map[followerId].add(followeeId)

    def unfollow(self, followerId, followeeId):
        self.follower_followees_map[followerId].discard(followeeId)

# V0 : TODO : fix getNewsFeed returned format
from collections import defaultdict

class Twitter(object):

    def __init__(self):

         self.users = []
         # {'id_1' : [foller_1, 2...], 'id_2' : [foller_3, 4...]..}
         self.follower_followees = defaultdict(set)
         # {'id_1' : [twitter_1, 2...], 'id_2' : [twitter_3, 4...]..}
         self.user_tweets = defaultdict(list)

    def postTweet(self, userId, tweetId):

        self.user_tweets[userId].append(tweetId)
        
    #TODO : fix this
    def getNewsFeed(self, userId):

        res = []
        for user in list(self.follower_followees[userId]) + [userId]:
            if user in self.user_tweets:
                res.append(self.user_tweets[userId])
                if len(res) >= 10:
                    break
            else:
                break
        return res[::-1]
        
    def follow(self, followerId, followeeId):

        self.follower_followees[followeeId].add(followeeId)
        
    def unfollow(self, followerId, followeeId):

        if followeeId in self.follower_followees[followerId]:
            idx = self.follower_followees[followeeId]
            self.follower_followees[followeeId].pop(idx)

# V0''
import collections, itertools, heapq
class Twitter(object):

    def __init__(self):
        self.timer = itertools.count(step=-1)
        self.tweets = collections.defaultdict(collections.deque)
        self.followees = collections.defaultdict(set)

    def postTweet(self, userId, tweetId):
        self.tweets[userId].appendleft((next(self.timer), tweetId))

    def getNewsFeed(self, userId):
        tweets = heapq.merge(*(self.tweets[u] for u in self.followees[userId] | {userId}))
        return [t for _, t in itertools.islice(tweets, 10)]

    def follow(self, followerId, followeeId):
        self.followees[followerId].add(followeeId)

    def unfollow(self, followerId, followeeId):
        self.followees[followerId].discard(followeeId)

# V1
# https://leetcode.com/problems/design-twitter/discuss/82943/Use-python-heapq.merge
# https://github.com/labuladong/fucking-algorithm/blob/master/%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84%E7%B3%BB%E5%88%97/%E8%AE%BE%E8%AE%A1Twitter.md
# IDEA : heapq.merge
from collections import defaultdict
from heapq import merge
class Twitter(object):
    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.follower_followees_map = defaultdict(set)
        self.user_tweets_map = defaultdict(list)
        self.time_stamp = 0

    def postTweet(self, userId, tweetId):
        """
        Compose a new tweet.
        :type userId: int
        :type tweetId: int
        :rtype: void
        """
        self.user_tweets_map[userId].append((self.time_stamp, tweetId))
        self.time_stamp -= 1

    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]
        """
        followees = self.follower_followees_map[userId]
        followees.add(userId)
        
        # reversed(.) returns a listreverseiterator, so the complexity is O(1) not O(n)
        candidate_tweets = [reversed(self.user_tweets_map[u]) for u in followees]

        tweets = []
        # complexity is 10lg(n), n is twitter's user number in worst case
        for t in merge(*candidate_tweets):
            tweets.append(t[1])
            if len(tweets) == 10:
                break
        return tweets

    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
        """
        self.follower_followees_map[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.follower_followees_map[followerId].discard(followeeId)

# V1'
# https://leetcode.com/problems/design-twitter/discuss/82863/Python-solution
# IDEA : collections.defaultdict
# * DEMO : itertools.count
# EXAMPLE 1
# In [23]: import itertools
#     ...: mytimer  = itertools.count(step=-1)
#     ...: print (mytimer)
#     ...: for _ in range(5):
#     ...:     print (next(mytimer))
#     ...:     
# count(0, -1)
# 0
# -1
# -2
# -3
# -4
# EXAMPLE 2 
# In [24]: import itertools
#     ...: mytimer2  = itertools.count(step=1)
#     ...: print (mytimer2)
#     ...: for _ in range(5):
#     ...:     print (next(mytimer2))
#     ...:     
# count(0)
# 0
# 1
# 2
# 3
# 4
# 
# * DEMO collections.defaultdict(collections.deque) :
# In [31]: mytweets = collections.defaultdict(collections.deque)
#     ...: mytweets['001'].appendleft(('1', 'twitterid_1'))
#     ...: mytweets['002'].appendleft(('2', 'twitterid_2'))
#     ...: mytweets['003'].appendleft(('3', 'twitterid_3'))
#     ...: mytweets['001'].appendleft(('10', 'twitterid_10'))
#     ...: print (mytweets)
#     ...: 
# defaultdict(<class 'collections.deque'>, {'001': deque([('10', 'twitterid_10'), ('1', 'twitterid_1')]), '002': deque([('2', 'twitterid_2')]), '003': deque([('3', 'twitterid_3')])})
# * DEMO heapq.merge(*iterables) : 
# https://www.geeksforgeeks.org/merge-two-sorted-arrays-python-using-heapq/
# heapq.merge(*iterables) -> Merge multiple sorted inputs into a single sorted output (for example, merge timestamped entries from multiple log files). Returns an iterator over the sorted values.
# In [46]: mytweets = collections.defaultdict(collections.deque)
#     ...: mytweets['1'].appendleft(('1', 'twitterid_1'))
#     ...: mytweets['2'].appendleft(('2', 'twitterid_2'))
#     ...: mytweets['3'].appendleft(('3', 'twitterid_3'))
#     ...: mytweets['1'].appendleft(('10', 'twitterid_10'))
#     ...: #print (mytweets)
#     ...: print (list(heapq.merge(*(mytweets[u] for u in ['1','2','3']))))
#     ...: print ('='*30)
#     ...: print (list(heapq.merge((mytweets[u] for u in ['1','2','3']))))
#     ...: 
# [('10', 'twitterid_10'), ('1', 'twitterid_1'), ('2', 'twitterid_2'), ('3', 'twitterid_3')]
# ==============================
# [deque([('10', 'twitterid_10'), ('1', 'twitterid_1')]), deque([('2', 'twitterid_2')]), deque([('3', 'twitterid_3')])]
# * DEMO : bitwise OR (a | b)
# ->  a | b  : bitwise OR  Each bit position in the result is the logical OR of the bits in the corresponding position of the operands. (1 if either is 1, otherwise 0.)
# https://realpython.com/python-operators-expressions/
# In [67]: 1 | 1
# Out[67]: 1

# In [68]: 1 | 2
# Out[68]: 3

# In [69]: 1 | 0
# Out[69]: 1
import collections, itertools, heapq
class Twitter(object):

    def __init__(self):
        self.timer = itertools.count(step=-1)
        self.tweets = collections.defaultdict(collections.deque)
        self.followees = collections.defaultdict(set)

    def postTweet(self, userId, tweetId):
        self.tweets[userId].appendleft((next(self.timer), tweetId))

    def getNewsFeed(self, userId):
        tweets = heapq.merge(*(self.tweets[u] for u in self.followees[userId] | {userId}))
        return [t for _, t in itertools.islice(tweets, 10)]

    def follow(self, followerId, followeeId):
        self.followees[followerId].add(followeeId)

    def unfollow(self, followerId, followeeId):
        self.followees[followerId].discard(followeeId)

# V1''
# https://blog.csdn.net/fuxuemingzhu/article/details/82155420
# IDEA : heapq
class User(object):
    """
    User structure
    """
    def __init__(self, userId):
        self.userId = userId
        self.tweets = set()
        self.following = set()

class Tweet(object):
    """
    Tweet structure
    """
    def __init__(self, tweetId, userId, ts):
        self.tweetId = tweetId
        self.userId = userId
        self.ts = ts
        
    def __cmp__(self, other):
        #call global(builtin) function cmp for int
        return cmp(other.ts, self.ts)

class Twitter(object):
    
    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.ts = 0
        self.userMap = dict()
        

    def postTweet(self, userId, tweetId):
        """
        Compose a new tweet.
        :type userId: int
        :type tweetId: int
        :rtype: void
        """
        if userId not in self.userMap:
            self.userMap[userId] = User(userId)
        tweet = Tweet(tweetId, userId, self.ts)
        self.userMap[userId].tweets.add(tweet)
        self.ts += 1

    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]
        """
        res = list()
        que = []
        if userId not in self.userMap:
            return res
        mainUser = self.userMap[userId]
        for t in mainUser.tweets:
            heapq.heappush(que, t)
        for u in mainUser.following:
            for t in u.tweets:
                heapq.heappush(que, t)
        n = 0
        while que and n < 10:
            res.append(heapq.heappop(que).tweetId)
            n += 1
        return res

    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 followeeId not in self.userMap:
            self.userMap[followeeId] = User(followeeId)
        if followerId not in self.userMap:
            self.userMap[followerId] = User(followerId)
        if followerId == followeeId:
            return
        followee = self.userMap[followeeId]
        self.userMap[followerId].following.add(followee)

    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
        """
        if (followerId == followeeId) or (followerId not in self.userMap) or (followeeId not in self.userMap):
            return
        followee = self.userMap[followeeId]
        if followee in self.userMap.get(followerId).following:
            self.userMap.get(followerId).following.remove(followee)

# V1'''
# https://www.hrwhisper.me/leetcode-design-twitter/
class Twitter(object):
    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.tweets_cnt = 0
        self.tweets = collections.defaultdict(list)
        self.follower_ship = collections.defaultdict(set)

    def postTweet(self, userId, tweetId):
        """
        Compose a new tweet.
        :type userId: int
        :type tweetId: int
        :rtype: void
        """
        self.tweets[userId].append([tweetId, self.tweets_cnt])
        self.tweets_cnt += 1

    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]
        """
        recent_tweets = []
        user_list = list(self.follower_ship[userId]) + [userId]
        userId_tweet_index = [[userId, len(self.tweets[userId]) - 1] for userId in user_list if userId in self.tweets]

        for _ in range(10):
            max_index = max_tweet_id = max_user_id = -1
            for i, (user_id, tweet_index) in enumerate(userId_tweet_index):
                if tweet_index >= 0:
                    tweet_info = self.tweets[user_id][tweet_index]
                    if tweet_info[1] > max_tweet_id:
                        max_index, max_tweet_id, max_user_id = i, tweet_info[1], user_id

            if max_index < 0: break
            recent_tweets.append(self.tweets[max_user_id][userId_tweet_index[max_index][1]][0])
            userId_tweet_index[max_index][1] -= 1

        return recent_tweets

    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.follower_ship[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
        """
        if followerId in self.follower_ship and followeeId in self.follower_ship[followerId]:
            self.follower_ship[followerId].remove(followeeId)

# V1''''
# http://bookshadow.com/weblog/2016/06/11/leetcode-design-twitter/
# IDEA : JAVA

# V2 
# https://github.com/kamyu104/LeetCode-Solutions/blob/master/Python/design-twitter.py
# Time:  O(klogu), k is most recently number of tweets,
#                  u is the number of the user's following.
# Space: O(t + f), t is the total number of tweets,
#                  f is the total number of followings.
import collections
import heapq
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)