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leetCode-335:Design Twitter

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问题描述

要求实现一个简单版的 Twitter。题目链接：**点我**

样例输入输出

输入：

[“Twitter”, “postTweet”, “getNewsFeed”, “follow”, “postTweet”, “getNewsFeed”, “unfollow”, “getNewsFeed”]
[[], [1, 5], [1], [1, 2], [2, 6], [1], [1, 2], [1]]

输出：

[null, null, [5], null, null, [6, 5], null, [5]]

解释：

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.

问题解法

此题是设计类型的题目，只要按要求实现即可。代码如下

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class Twitter {
    class Tweet {
        private int tweetId;
        private int userId;

        public Tweet(int tweetId, int userId) {
            this.tweetId = tweetId;
            this.userId = userId;
        }

        public int getTweetId() {
            return tweetId;
        }

        public int getUserId() {
            return userId;
        }
    }

    private List<Tweet> tweets = new LinkedList<>();

    private Map<Integer, Set<Integer>> followMap = new HashMap<>();

    public Twitter() {

    }

    public void postTweet(int userId, int tweetId) {
        tweets.add(0, new Tweet(tweetId, userId));
    }

    public List<Integer> getNewsFeed(int userId) {
        Set<Integer> followSet = followMap.getOrDefault(userId, new HashSet<>());
        List<Integer> result = new ArrayList<>(10);
        int count = 0;
        for (Tweet tweet : tweets) {
            int tweetUserId = tweet.getUserId();
            if (tweetUserId == userId || followSet.contains(tweetUserId)) {
                result.add(tweet.getTweetId());
                count++;
                if (count == 10) {
                    break;
                }
            }
        }

        return result;
    }

    public void follow(int followerId, int followeeId) {
        Set<Integer> followSet = followMap.getOrDefault(followerId, new HashSet<>());
        followSet.add(followeeId);
        followMap.put(followerId, followSet);
    }

    public void unfollow(int followerId, int followeeId) {
        Set<Integer> followSet = followMap.getOrDefault(followerId, new HashSet<>());
        followSet.remove(followeeId);
    }
}

/**
 * Your Twitter object will be instantiated and called as such:
 * Twitter obj = new Twitter();
 * obj.postTweet(userId,tweetId);
 * List<Integer> param_2 = obj.getNewsFeed(userId);
 * obj.follow(followerId,followeeId);
 * obj.unfollow(followerId,followeeId);
 */