add 355 Design Twitter

selfboot · selfboot · commit 897166acd431 · 2016-07-08T15:13:20.000+08:00
diff --git a/Combination/355_DesignTwitter.cpp b/Combination/355_DesignTwitter.cpp
@@ -0,0 +1,85 @@
+/*
+ * @Author: xuezaigds@gmail.com
+ * @Last Modified time: 2016-07-08 15:10:06
+ */
+
+class Twitter {
+    struct Tweet
+    {
+        int time;
+        int id;
+        Tweet(int time, int id) : time(time), id(id) {}
+    };
+
+    struct compare{
+        bool operator()(const Tweet x, const Tweet y) {
+            return x.time < y.time;
+        }
+    };
+
+    int time;
+    unordered_map<int, vector<Tweet>> tweets;
+    unordered_map<int, unordered_set<int>> followees;
+
+public:
+    /** Initialize your data structure here. */
+    Twitter(): time(0) {
+    }
+
+    /** Compose a new tweet. */
+    void postTweet(int userId, int tweetId) {
+        tweets[userId].push_back(Tweet(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) {
+        priority_queue<Tweet, vector<Tweet>, compare> allnews;
+        for(auto u: followees[userId]){
+            for(auto &t: tweets[u]){
+                allnews.push(t);
+            }
+        }
+        for(auto &t: tweets[userId]){
+            allnews.push(t);
+        }
+        vector<int> ans;
+        for(int i=0; i<10 && !allnews.empty(); i++){
+            ans.push_back(allnews.top().id);
+            allnews.pop();
+        }
+        return ans;
+    }
+
+    /** Follower follows a followee. If the operation is invalid,
+    it should be a no-op. */
+    void follow(int followerId, int followeeId) {
+        if(followerId != followeeId){
+            followees[followerId].insert(followeeId);
+        }
+    }
+
+    /** Follower unfollows a followee. If the operation is invalid,
+    it should be a no-op. */
+    void unfollow(int followerId, int followeeId) {
+        followees[followerId].erase(followeeId);
+    }
+};
+
+/**
+ * Your Twitter object will be instantiated and called as such:
+ * Twitter obj = new Twitter();
+ * obj.postTweet(userId,tweetId);
+ * vector<int> param_2 = obj.getNewsFeed(userId);
+ * obj.follow(followerId,followeeId);
+ * obj.unfollow(followerId,followeeId);
+ */
+
+/*
+["Twitter","postTweet","postTweet","getNewsFeed","postTweet","getNewsFeed"]
+[[],[1,5],[1,3],[3,5],[1,6],[3,5,6]]
+["Twitter","postTweet","getNewsFeed","follow","postTweet","getNewsFeed","unfollow","getNewsFeed"]
+[[],[1,5],[1],[1,2],[2,6],[1],[1,2],[1]]
+*/
diff --git a/Combination/355_DesignTwitter.py b/Combination/355_DesignTwitter.py
@@ -0,0 +1,56 @@
+#! /usr/bin/env python
+# -*- coding: utf-8 -*-
+# @Author: xuezaigds@gmail.com
+# @Last Modified time: 2016-07-08 13:57:50
+
+
+class Twitter(object):
+    """
+    Accordting to:
+    https://discuss.leetcode.com/topic/47838/python-solution
+    """
+    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):
+        """Compose a new tweet.
+        """
+        self.tweets[userId].appendleft((next(self.timer), 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.
+        """
+        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):
+        """Follower follows a followee. If the operation is invalid, it should be a no-op.
+        """
+        self.followees[followerId].add(followeeId)
+
+    def unfollow(self, followerId, followeeId):
+        """Follower unfollows a followee. If the operation is invalid, it should be a no-op.
+        """
+        self.followees[followerId].discard(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)
+
+"""
+["Twitter","postTweet","postTweet","getNewsFeed","postTweet","getNewsFeed"]
+[[],[1,5],[1,3],[3,5],[1,6],[3,5,6]]
+["Twitter","postTweet","getNewsFeed","follow","postTweet","getNewsFeed","unfollow","getNewsFeed"]
+[[],[1,5],[1],[1,2],[2,6],[1],[1,2],[1]]
+"""
diff --git a/README.md b/README.md
@@ -307,6 +307,7 @@
 * 146. [LRU Cache](Combination/146_LRUCache.py)
 * 300. [Longest Increasing Subsequence](Combination/300_LongestIncreasingSubsequence.py)
 * 329. [Longest Increasing Path in a Matrix](Combination/329_LongestIncreasingPathInMatrix.py)
+* 355. [Design Twitter](Combination/355_DesignTwitter.py)
 
 # DFA
 
