LeetCode-in-Java

1348. Tweet Counts Per Frequency

Medium

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 <= 109
• 0 <= endTime - startTime <= 104
• There will be at most 104 calls in total to recordTweet and getTweetCountsPerFrequency.

Solution

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class TweetCounts {

    private static class TreeNode {
        private int val;
        private TreeNode left;
        private TreeNode right;

        private TreeNode(int data) {
            val = data;
            left = null;
            right = null;
        }
    }

    private Map<String, TreeNode> map = new HashMap<>();

    private TreeNode insert(TreeNode root, int val) {
        if (root == null) {
            root = new TreeNode(val);
        } else if (root.val <= val) {
            root.right = insert(root.right, val);
        } else {
            root.left = insert(root.left, val);
        }
        return root;
    }

    public void recordTweet(String name, int time) {
        TreeNode root = map.get(name);
        root = insert(root, time);
        map.put(name, root);
    }

    private int treverse(TreeNode root, int l, int r) {
        if (root == null || l >= r) {
            return 0;
        }
        if (root.val <= l) {
            int add = root.val == l ? 1 : 0;
            return add + treverse(root.right, l, r);
        }
        if (root.val >= r) {
            return treverse(root.left, l, r);
        }
        return 1 + treverse(root.left, l, r) + treverse(root.right, l, r);
    }

    public List<Integer> getTweetCountsPerFrequency(String freq, String name, int start, int end) {
        int d = 0;
        TreeNode root = map.get(name);
        List<Integer> res = new ArrayList<>();
        if (freq.equals("minute")) {
            d = 60;
        } else if (freq.equals("hour")) {
            d = 3600;
        } else {
            d = 86400;
        }
        while (start + d <= end) {
            int count = treverse(root, start, start + d);
            start = start + d;
            res.add(count);
        }
        if (start <= end) {
            int count = treverse(root, start, end + 1);
            res.add(count);
        }
        return res;
    }
}

/*
 * 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);
 */

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