Find Trending Hashtags

Find Trending Hashtags - Problem

Database Medium

Given a table Tweets containing user tweets with hashtags, find the top 3 trending hashtags in February 2024.

Requirements:

Each tweet contains exactly one hashtag
Filter tweets from February 2024 only
Return top 3 hashtags by count
Order results by hashtag count (descending), then by hashtag name (descending)

Table Schema

Tweets

Column Name	Type	Description
`user_id`	int	ID of the user who posted the tweet
`tweet_id` PK	int	Primary key, unique identifier for each tweet
`tweet_date`	date	Date when the tweet was posted
`tweet` PK	varchar	Content of the tweet containing one hashtag

Primary Key: tweet_id

Note: Each tweet contains exactly one hashtag that needs to be extracted and counted

Input & Output

Example 1 — Basic Hashtag Counting

Input Table:

user_id	tweet_id	tweet_date	tweet
1	101	2024-02-01	Love this #AI trend!
2	102	2024-02-02	Working on #AI project
3	103	2024-02-03	Excited about #tech
4	104	2024-02-04	New #blockchain news
5	105	2024-02-05	Learning #AI today
6	106	2024-01-30	January #AI post

Output:

hashtag	hashtag_count
#AI	3
#tech	1
#blockchain	1

💡 Note:

From the February 2024 tweets, #AI appears 3 times (most frequent), while #tech and #blockchain each appear once. The January tweet is excluded. Results are ordered by count DESC, then hashtag DESC, so #tech comes before #blockchain alphabetically in descending order.

Example 2 — Tie Breaking by Hashtag Name

Input Table:

user_id	tweet_id	tweet_date	tweet
1	201	2024-02-01	Love #python coding
2	202	2024-02-02	Great #java tutorial
3	203	2024-02-03	Amazing #react framework
4	204	2024-02-04	Building with #nodejs

Output:

hashtag	hashtag_count
#react	1
#python	1
#nodejs	1

💡 Note:

All hashtags have the same count (1), so they are ordered by hashtag name in descending order: #react, #python, #nodejs, #java. Only the top 3 are returned.

Constraints

1 ≤ user_id ≤ 10000
tweet_id is unique for each row
tweet_date is in YYYY-MM-DD format
Each tweet contains exactly one hashtag starting with #
Hashtag can contain letters, numbers, and underscores

Visualization

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Asked in

M Meta 38 T Twitter 45 L LinkedIn 28

Use date filtering to get February 2024 tweets, string functions to extract hashtags, then GROUP BY and COUNT(*) to find trending hashtags.

Table Schema

Tweets

Column Name	Type	Description
`user_id`	int	ID of the user who posted the tweet
`tweet_id` PK	int	Primary key, unique identifier for each tweet
`tweet_date`	date	Date when the tweet was posted
`tweet` PK	varchar	Content of the tweet containing one hashtag

Primary Key: tweet_id

Note: Each tweet contains exactly one hashtag that needs to be extracted and counted

Common Approaches

✓ String Extraction with GROUP BY

⏱️ Time: O(n log n) Space: O(k)

Filter tweets by February 2024 date range, extract hashtags from tweet text using string functions, group by hashtag and count occurrences, then order by count and hashtag name to get top 3.

String Extraction with GROUP BY — Algorithm Steps

Step 1: Filter tweets from February 2024 using date conditions
Step 2: Extract hashtags from tweet text using string functions
Step 3: Group by hashtag and count occurrences
Step 4: Order by count DESC, hashtag DESC and limit to top 3

Visualization

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Step-by-Step Walkthrough

Filter

Select February 2024 tweets

Extract

Extract hashtags from text

Group & Count

Group by hashtag and count

Code -

solution.c — C

Time & Space Complexity

Time Complexity

⏱️

O(n log n)

Filtering and sorting the grouped results

⚡ Linearithmic

Space Complexity

O(k)

Space for unique hashtags (k distinct hashtags)

✓ Linear Space

28.5K Views

Medium Frequency

~12 min Avg. Time

892 Likes

Ln 1, Col 1

Smart Actions

💡 Explanation

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Table Schema

Input & Output

Constraints

Visualization

Related Problems

Table Schema

Common Approaches

String Extraction with GROUP BY — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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