[LeetCode] 335. Design Twitter

 Problem : https://leetcode.com/problems/design-twitter/

- Tweet be posted later may have smaller tweetId. So we need to save the time when the tweet be post.

- Should not allow user to follow themselves.

- Should not allow user to unfollow not-followed user.

from operator import itemgetter

class Twitter:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.timer = 1
        self.follows = defaultdict(set)
        self.tweets = defaultdict(list)

    def postTweet(self, userId: int, tweetId: int) -> None:
        """
        Compose a new tweet.
        """
        self.tweets[userId].append((self.timer, tweetId))
        self.timer += 1
        

    def getNewsFeed(self, userId: int) -> List[int]:
        """
        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.
        """
        
        allTweets = self.tweets[userId][:]
        
        for f in self.follows[userId]:
            allTweets.extend(self.tweets[f])
            
        
        allTweets.sort(reverse = True, key = itemgetter(0))
        allTweets = allTweets if len(allTweets) <= 10 else allTweets[:10]
        
        return [tweetId for _, tweetId in allTweets]
                

    def follow(self, followerId: int, followeeId: int) -> None:
        """
        Follower follows a followee. If the operation is invalid, it should be a no-op.
        """
        
        if followerId != followeeId:
            self.follows[followerId].add(followeeId)
        

    def unfollow(self, followerId: int, followeeId: int) -> None:
        """
        Follower unfollows a followee. If the operation is invalid, it should be a no-op.
        """
        
        if followerId != followeeId and followeeId in self.follows[followerId]:
            self.follows[followerId].remove(followeeId)
        


# Your Twitter object will be instantiated and called as such:
# obj = Twitter()
# obj.postTweet(userId,tweetId)
# param_2 = obj.getNewsFeed(userId)
# obj.follow(followerId,followeeId)
# obj.unfollow(followerId,followeeId)