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Invalid Tweets

Table: Tweets

+----------------+---------+
| Column Name    | Type    |
+----------------+---------+
| tweet_id       | int     |
| content        | varchar |
+----------------+---------+
tweet_id is the primary key (column with unique values) for this table.
content consists of characters on an American Keyboard, and no other special characters.
This table contains all the tweets in a social media app.

 

Write a solution to find the IDs of the invalid tweets. The tweet is invalid if the number of characters used in the content of the tweet is strictly greater than 15.

Return the result table in any order.

The result format is in the following example.

 

Example 1:

Input: 
Tweets table:
+----------+-----------------------------------+
| tweet_id | content                           |
+----------+-----------------------------------+
| 1        | Let us Code                       |
| 2        | More than fifteen chars are here! |
+----------+-----------------------------------+
Output: 
+----------+
| tweet_id |
+----------+
| 2        |
+----------+
Explanation: 
Tweet 1 has length = 11. It is a valid tweet.
Tweet 2 has length = 33. It is an invalid tweet.

Solution Explanation for LeetCode Problem 1683: Invalid Tweets

This problem requires identifying tweets whose content exceeds 15 characters. The solution leverages SQL's string length function to achieve this efficiently.

Approach

The core idea is to filter the Tweets table based on the length of the content column. We use the appropriate string length function (CHAR_LENGTH in MySQL) to determine the number of characters in each tweet. Then, we select only the tweet_id where the length is strictly greater than 15.

SQL Code (MySQL)

SELECT
    tweet_id
FROM Tweets
WHERE CHAR_LENGTH(content) > 15;

This query directly filters the Tweets table. CHAR_LENGTH(content) calculates the length of the content string for each row. The WHERE clause filters the results to include only those rows where the length is greater than 15. The query then returns only the tweet_id column for those invalid tweets.

Time and Space Complexity Analysis

  • Time Complexity: O(N), where N is the number of rows in the Tweets table. The database system needs to iterate through each row to calculate the length of the content and apply the filter. The CHAR_LENGTH function is generally efficient and optimized within the database system.

  • Space Complexity: O(M), where M is the number of invalid tweets. The space used is primarily to store the resulting tweet_id values. In the worst case (all tweets are invalid), M would be equal to N. However, the space used for intermediate calculations by the database system is generally not considered part of the algorithm's space complexity. The space complexity is dominated by the output size.

While other approaches exist, they are less efficient than the direct SQL query approach described above:

  • Procedural approach: A procedural approach using loops and string length checks within a stored procedure would be far less efficient due to the overhead of procedural execution within a database.

  • Fetching all data into application code: Fetching all tweets into application memory and processing them there would be significantly less efficient, especially for large tables, due to the increased network and memory overhead.

The presented SQL solution directly utilizes the database's optimized string functions and filtering capabilities, offering the most efficient approach to solve this problem.