Generate Tag for Video Caption - Practice Coding Problems

Generate Tag for Video Caption - Problem

String Simulation Easy

Generate Tag for Video Caption

You're building a social media platform where users upload videos with captions. To help with content discovery and trending algorithms, you need to automatically generate hashtags from video captions.

Given a string caption representing the caption for a video, transform it into a valid hashtag by performing these operations in order:

1. Convert to camelCase: Combine all words into a single string where the first word is lowercase and subsequent words have their first letter capitalized
2. Add hashtag prefix: Prefix the result with '#'
3. Remove non-English letters: Keep only English letters (a-z, A-Z) and the '#' symbol
4. Truncate: Limit the final result to maximum 100 characters

Example: "Hello World! 123" → "#helloWorld"

Return the generated hashtag after applying all transformations.

Input & Output

example_1.py — Basic camelCase conversion

$ Input: caption = "Hello World"

› Output: "#helloWorld"

💡 Note: Convert to camelCase (hello + World), add # prefix, no special characters to remove, result is under 100 chars

example_2.py — With special characters

$ Input: caption = "Amazing Video! 2024"

› Output: "#amazingVideo"

💡 Note: Convert to camelCase (amazing + Video), add # prefix, remove '!', '2024', and spaces, result is '#amazingVideo'

example_3.py — Long caption truncation

$ Input: caption = "This Is A Very Long Video Caption That Should Be Truncated Because It Exceeds The Maximum Character Limit"

› Output: "#thisIsAVeryLongVideoCaptionThatShouldBeTruncatedBecauseItExceedsTheMaximumCharacterLimit"

💡 Note: Convert to camelCase, add # prefix, no special characters, but result would be longer than 100 characters so it gets truncated at position 100

Visualization

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Understanding the Visualization

Start with #

Initialize result with hashtag symbol

Process First Word

Convert first word to all lowercase

Handle Word Boundaries

Detect spaces to identify new words

Capitalize New Words

Make first letter of subsequent words uppercase

Filter Characters

Skip numbers and special characters

Check Length Limit

Stop at 100 characters to meet platform requirements

Key Takeaway

🎯 Key Insight: Process everything in one pass - track word boundaries with a boolean flag, apply camelCase formatting on-the-fly, filter unwanted characters, and stop at 100 characters for optimal O(n) performance.

Time & Space Complexity

Time Complexity

⏱️

O(n)

Single pass through input string, each character processed once

✓ Linear Growth

Space Complexity

O(1)

Only the result string builder, no intermediate data structures needed

✓ Linear Space

Constraints

1 ≤ caption.length ≤ 1000
caption consists of English letters, spaces, digits, and punctuation marks
The result must not exceed 100 characters
At least one English letter must be present in the caption

Asked in

f Meta 45 T TikTok 38 📷 Instagram 32 ▶ YouTube 28 🐦 Twitter 25

The optimal solution processes the caption in a single pass using a string builder. We iterate through each character, applying camelCase formatting (lowercase first word, capitalize subsequent words), filtering non-alphabetic characters, and respecting the 100-character limit simultaneously. This achieves O(n) time complexity and O(1) extra space complexity.

Common Approaches

Approach	Time	Space	Notes
✓ Multiple Pass String Processing	O(n²)	O(n)	Process the string in multiple separate passes for each transformation
Single Pass String Builder (Optimal)	O(n)	O(1)	Process all transformations in a single pass using a string builder

Multiple Pass String Processing — Algorithm Steps

Split the caption into words using spaces
Convert first word to lowercase, capitalize first letter of subsequent words
Join all words together
Add '#' prefix
Remove all non-English letter characters except '#'
Truncate to 100 characters if needed

Visualization

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Step-by-Step Walkthrough

Split Words

Split 'Hello World! 123' into ['Hello', 'World!', '123']

CamelCase

Convert to 'helloWorld!123'

Add Hashtag

Prefix with '#' to get '#helloWorld!123'

Clean Characters

Remove non-letters to get '#helloWorld'

Truncate

Ensure length ≤ 100 characters

Code -

solution.c — C

#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <stdlib.h>

char* generateHashtag(char* caption) {
    char* words[1000];
    int wordCount = 0;
    
    // Step 1: Split into words
    char* token = strtok(caption, " ");
    while (token != NULL && wordCount < 1000) {
        words[wordCount++] = token;
        token = strtok(NULL, " ");
    }
    
    char* result = (char*)malloc(1001 * sizeof(char));
    strcpy(result, "#");
    
    // Step 2: Convert to camelCase
    for (int i = 0; i < wordCount; i++) {
        int len = strlen(words[i]);
        if (i == 0) {
            for (int j = 0; j < len; j++) {
                words[i][j] = tolower(words[i][j]);
            }
        } else {
            words[i][0] = toupper(words[i][0]);
            for (int j = 1; j < len; j++) {
                words[i][j] = tolower(words[i][j]);
            }
        }
        strcat(result, words[i]);
    }
    
    // Step 4: Remove non-English letters
    char* cleanResult = (char*)malloc(1001 * sizeof(char));
    int idx = 0;
    for (int i = 0; result[i] != '\0' && idx < 100; i++) {
        if (result[i] == '#' || isalpha(result[i])) {
            cleanResult[idx++] = result[i];
        }
    }
    cleanResult[idx] = '\0';
    
    free(result);
    return cleanResult;
}

Time & Space Complexity

Time Complexity

⏱️

O(n²)

Multiple passes through string, plus string concatenation operations that can be O(n) each

⚠ Quadratic Growth

Space Complexity

O(n)

Stores multiple intermediate string versions during processing

⚡ Linearithmic Space

Constraints

1 ≤ caption.length ≤ 1000
caption consists of English letters, spaces, digits, and punctuation marks
The result must not exceed 100 characters
At least one English letter must be present in the caption

58.2K Views

Medium Frequency

~15 min Avg. Time

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Input & Output

Visualization

Time & Space Complexity

Related Problems

Constraints

Common Approaches

Multiple Pass String Processing — Algorithm Steps

Visualization

Code -

Time & Space Complexity

Constraints

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