Invalid Tweets - Practice Coding Problems

Invalid Tweets - Problem

Database Easy

Find Invalid Tweets

Imagine you're working as a backend engineer for a social media platform that has strict content policies. Your platform enforces a 15-character limit for all tweets to keep conversations concise and engaging.

You have access to a Tweets table containing all user posts. Your task is to identify and return the IDs of all invalid tweets - those that exceed the 15-character limit.

Table Schema:
Tweets
+----------------+---------+
| Column Name    | Type    |
+----------------+---------+
| tweet_id       | int     |
| content        | varchar |
+----------------+---------+

Goal: Write a SQL query to find all tweet IDs where the content length is strictly greater than 15 characters.

Note: The content can contain alphanumeric characters, exclamation marks (!), and spaces - no other special characters are allowed.

Input & Output

example_1.sql — Basic Example

$ Input: Tweets table: +----------+-----------------------------------+ | tweet_id | content | +----------+-----------------------------------+ | 1 | Vote for Biden | | 2 | Let us make America great again! | +----------+-----------------------------------+

› Output: +----------+ | tweet_id | +----------+ | 2 | +----------+

💡 Note: Tweet 1: 'Vote for Biden' has 14 characters (≤ 15) → Valid. Tweet 2: 'Let us make America great again!' has 32 characters (> 15) → Invalid.

example_2.sql — Edge Cases

$ Input: Tweets table: +----------+-----------------+ | tweet_id | content | +----------+-----------------+ | 3 | Exactly 15 char | | 4 | Exactly 16 chars| | 5 | Short | +----------+-----------------+

› Output: +----------+ | tweet_id | +----------+ | 4 | +----------+

💡 Note: Tweet 3: Exactly 15 characters (= 15) → Valid. Tweet 4: 16 characters (> 15) → Invalid. Tweet 5: 5 characters (< 15) → Valid.

example_3.sql — All Valid Tweets

$ Input: Tweets table: +----------+---------+ | tweet_id | content | +----------+---------+ | 6 | Hi | | 7 | Good | | 8 | Morning | +----------+---------+

› Output: +----------+ | tweet_id | +----------+ +----------+

💡 Note: All tweets have ≤ 15 characters, so no invalid tweets are found. The result table is empty.

Visualization

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Understanding the Visualization

Load Tweets

Database loads all tweets from the Tweets table

Apply LENGTH()

SQL LENGTH() function calculates character count for each content

Filter Results

WHERE clause filters tweets with length > 15

Return IDs

SELECT returns only the tweet_id column of invalid tweets

Key Takeaway

🎯 Key Insight: SQL's LENGTH() function provides instant character counting, making this a simple one-liner: `SELECT tweet_id FROM Tweets WHERE LENGTH(content) > 15`

Time & Space Complexity

Time Complexity

⏱️

O(n × m)

Where n is number of tweets and m is average content length

✓ Linear Growth

Space Complexity

O(1)

Only storing current count and result

✓ Linear Space

Constraints

1 ≤ tweet_id ≤ 10⁶
1 ≤ content.length ≤ 100
content consists only of alphanumeric characters, exclamation marks (!), and spaces
Each tweet_id is unique (primary key)

Asked in

🐦 Twitter 85 f Meta 42 🎵 TikTok 38 in LinkedIn 25

The optimal solution uses SQL's LENGTH() function to efficiently count characters in each tweet's content. Simply filter tweets where LENGTH(content) > 15 and return their IDs. This approach is O(n) time complexity and leverages the database engine's optimized string functions.

Common Approaches

Approach	Time	Space	Notes
✓ Manual Character Counting (Brute Force)	O(n × m)	O(1)	Manually examine each tweet and count characters individually

Manual Character Counting (Brute Force) — Algorithm Steps

Read each tweet from the database one by one
For each tweet, manually count every character in the content
Compare the count with 15
If count > 15, add tweet_id to result list

Visualization

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Step-by-Step Walkthrough

Select Tweet

Pick the first tweet to examine

Count Characters

Manually count each character: 1, 2, 3, 4...

Compare with Limit

Check if count > 15

Record Result

Add to invalid list if exceeds limit

Code -

solution.c — C

// Simulating manual character counting approach
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct {
    int tweet_id;
    char* content;
} Tweet;

int* findInvalidTweetsManual(Tweet* tweets, int n, int* returnSize) {
    int* invalidIds = malloc(n * sizeof(int));
    *returnSize = 0;
    
    for (int i = 0; i < n; i++) {
        int tweetId = tweets[i].tweet_id;
        char* content = tweets[i].content;
        
        // Manual character counting
        int charCount = 0;
        for (int j = 0; content[j] != '\0'; j++) {
            charCount++;
        }
        
        // Check if invalid
        if (charCount > 15) {
            invalidIds[(*returnSize)++] = tweetId;
        }
    }
    
    return invalidIds;
}

Time & Space Complexity

Time Complexity

⏱️

O(n × m)

Where n is number of tweets and m is average content length

✓ Linear Growth

Space Complexity

O(1)

Only storing current count and result

✓ Linear Space

Constraints

1 ≤ tweet_id ≤ 10⁶
1 ≤ content.length ≤ 100
content consists only of alphanumeric characters, exclamation marks (!), and spaces
Each tweet_id is unique (primary key)

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Input & Output

Visualization

Time & Space Complexity

Related Problems

Constraints

Common Approaches

Manual Character Counting (Brute Force) — Algorithm Steps

Visualization

Code -

Time & Space Complexity

Constraints

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