1348. Tweet Counts Per Frequency

Problem

A social media company is trying to monitor activity on their site by analyzing the number of tweets that occur in select periods of time. These periods can be partitioned into smaller time chunks based on a certain frequency (every minute, hour, or day).

For example, the period [10, 10000] (in seconds) would be partitioned into the following time chunks with these frequencies:

• Every minute (60-second chunks): [10,69], [70,129], [130,189], ..., [9970,10000]

• Every hour (3600-second chunks): [10,3609], [3610,7209], [7210,10000]

• Every day (86400-second chunks): [10,10000]

Notice that the last chunk may be shorter than the specified frequency's chunk size and will always end with the end time of the period (10000 in the above example).

Design and implement an API to help the company with their analysis.

Implement the TweetCounts class:

• TweetCounts() Initializes the TweetCounts object.

• void recordTweet(String tweetName, int time) Stores the tweetName at the recorded time (in seconds). List<Integer> getTweetCountsPerFrequency(String freq, String tweetName, int startTime, int endTime) Returns a list of integers representing the number of tweets with tweetName in each time chunk for the given period of time [startTime, endTime] (in seconds) and frequency freq.

• freq is one of "minute", "hour", or "day" representing a frequency of every minute, hour, or day respectively.

  Example:

Input
["TweetCounts","recordTweet","recordTweet","recordTweet","getTweetCountsPerFrequency","getTweetCountsPerFrequency","recordTweet","getTweetCountsPerFrequency"]
[[],["tweet3",0],["tweet3",60],["tweet3",10],["minute","tweet3",0,59],["minute","tweet3",0,60],["tweet3",120],["hour","tweet3",0,210]]

Output
[null,null,null,null,[2],[2,1],null,[4]]

Explanation
TweetCounts tweetCounts = new TweetCounts();
tweetCounts.recordTweet("tweet3", 0);                              // New tweet "tweet3" at time 0
tweetCounts.recordTweet("tweet3", 60);                             // New tweet "tweet3" at time 60
tweetCounts.recordTweet("tweet3", 10);                             // New tweet "tweet3" at time 10
tweetCounts.getTweetCountsPerFrequency("minute", "tweet3", 0, 59); // return [2]; chunk [0,59] had 2 tweets
tweetCounts.getTweetCountsPerFrequency("minute", "tweet3", 0, 60); // return [2,1]; chunk [0,59] had 2 tweets, chunk [60,60] had 1 tweet
tweetCounts.recordTweet("tweet3", 120);                            // New tweet "tweet3" at time 120
tweetCounts.getTweetCountsPerFrequency("hour", "tweet3", 0, 210);  // return [4]; chunk [0,210] had 4 tweets

  Constraints:

• 0 <= time, startTime, endTime <= 10^9

• 0 <= endTime - startTime <= 10^4

• There will be at most 10^4 calls in total to recordTweet and getTweetCountsPerFrequency.

Solution (Java)

class TweetCounts {
    private static final int MINUTE = 60;
    private static final int HOUR = 3600;
    private static final int DAY = 86400;

    private final Map<String, Map<Integer, Map<Integer, Map<Integer, List<Integer>>>>> store;

    public TweetCounts() {
        this.store = new HashMap<>();
    }

    public void recordTweet(String tweetName, int time) {
        int d = time / DAY;
        int h = (time - d * DAY) / HOUR;
        int m = (time - d * DAY - h * HOUR) / MINUTE;
        Map<Integer, Map<Integer, Map<Integer, List<Integer>>>> dstore =
                store.computeIfAbsent(tweetName, k -> new HashMap<>());
        Map<Integer, Map<Integer, List<Integer>>> hstore =
                dstore.computeIfAbsent(d, k -> new HashMap<>());
        Map<Integer, List<Integer>> mstore = hstore.computeIfAbsent(h, k -> new HashMap<>());
        mstore.computeIfAbsent(m, k -> new ArrayList<>()).add(time);
    }

    public List<Integer> getTweetCountsPerFrequency(
            String freq, String tweetName, int startTime, int endTime) {
        int sfreq = convFreqToSecond(freq);
        Map<Integer, Map<Integer, Map<Integer, List<Integer>>>> dstore = store.get(tweetName);
        int[] chunks = new int[(endTime - startTime) / sfreq + 1];
        int sd = startTime / DAY;
        int ed = endTime / DAY;
        for (int d = sd; d <= ed; d++) {
            if (!dstore.containsKey(d)) {
                continue;
            }
            int sh = startTime <= (d * DAY) ? 0 : ((startTime - d * DAY) / HOUR);
            int eh = endTime > ((d + 1) * DAY) ? (DAY / HOUR) : ((endTime - d * DAY) / HOUR + 1);
            Map<Integer, Map<Integer, List<Integer>>> hstore = dstore.get(d);
            for (int h = sh; h < eh; h++) {
                if (!hstore.containsKey(h)) {
                    continue;
                }
                int sm =
                        startTime <= (d * DAY + h * HOUR)
                                ? 0
                                : ((startTime - d * DAY - h * HOUR) / MINUTE);
                int em =
                        endTime > (d * DAY + (h + 1) * HOUR)
                                ? (HOUR / MINUTE)
                                : ((endTime - d * DAY - h * HOUR) / MINUTE + 1);
                Map<Integer, List<Integer>> mstore = hstore.get(h);
                for (int m = sm; m <= em; m++) {
                    if (!mstore.containsKey(m)) {
                        continue;
                    }
                    for (Integer rc : mstore.get(m)) {
                        if (startTime <= rc && rc <= endTime) {
                            chunks[(rc - startTime) / sfreq]++;
                        }
                    }
                }
            }
        }
        List<Integer> ans = new ArrayList<>();
        for (int chunk : chunks) {
            ans.add(chunk);
        }
        return ans;
    }

    private int convFreqToSecond(String freq) {
        switch (freq) {
            case "minute":
                return MINUTE;
            case "hour":
                return HOUR;
            case "day":
                return DAY;
            default:
                return 0;
        }
    }
}

/**
 * Your TweetCounts object will be instantiated and called as such:
 * TweetCounts obj = new TweetCounts();
 * obj.recordTweet(tweetName,time);
 * List<Integer> param_2 = obj.getTweetCountsPerFrequency(freq,tweetName,startTime,endTime);
 */

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).