LeetCode 3087: Find Trending Hashtags Solution

Master LeetCode problem 3087 (Find Trending Hashtags), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

3087. Find Trending Hashtags

Medium

Database

Problem Explanation

Explanation:

To find the trending hashtags, we can use a hashmap to store the frequency of each hashtag. After parsing all the tweets and extracting hashtags, we can sort the hashtags based on their frequencies and return the top k trending hashtags.

Algorithm:

Initialize a hashmap to store the frequency of each hashtag.
Parse each tweet and extract the hashtags.
Update the frequency of each hashtag in the hashmap.
Sort the hashtags based on their frequencies in descending order.
Return the top k trending hashtags.

Time Complexity:

Parsing tweets: O(n), where n is the total number of characters in all tweets.
Updating frequency in hashmap: O(m), where m is the number of unique hashtags.
Sorting hashtags: O(m log m), where m is the number of unique hashtags.
Total time complexity: O(n + m log m)

Space Complexity:

Space required for the hashmap to store frequency: O(m)

Solution Code

import java.util.*;

class Solution {
    public List<String> findTrendingHashtags(List<String> tweets, int k) {
        Map<String, Integer> hashtagFreq = new HashMap<>();
        
        for (String tweet : tweets) {
            String[] words = tweet.split(" ");
            for (String word : words) {
                if (word.startsWith("#")) {
                    String hashtag = word.substring(1);
                    hashtagFreq.put(hashtag, hashtagFreq.getOrDefault(hashtag, 0) + 1);
                }
            }
        }
        
        List<String> trendingHashtags = new ArrayList<>(hashtagFreq.keySet());
        Collections.sort(trendingHashtags, (a, b) -> {
            if (hashtagFreq.get(a).equals(hashtagFreq.get(b))) {
                return a.compareTo(b);
            }
            return hashtagFreq.get(b) - hashtagFreq.get(a);
        });
        
        return trendingHashtags.subList(0, Math.min(k, trendingHashtags.size()));
    }
}

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