🦄 Runic Compression: Run-Length Encoding

Difficulty: Beginner Tags: strings, compression, iteration, encoding Series: CS 102: Problem Solving & Logic

Problem

Ancient scholars compress their runic texts using run-length encoding. Transform consecutive identical characters into a compact format.

Implement run-length encoding: compress sequences of consecutive identical characters into the format <character><count>. Even single characters should include their count of 1.

Real-World Application

Run-length encoding appears in: - Image compression - BMP, TIFF file formats for simple graphics - Data transmission - reducing bandwidth for repetitive data - Fax machines - compressing black and white documents - Video compression - early codecs, animation compression - Genetic sequencing - compressing DNA sequences - Network protocols - compressing repetitive packet data - Database storage - column-oriented databases - Text compression - preprocessing step for other algorithms

Input

data = str  # String to compress

Output

str  # Run-length encoded string

Constraints

• String length ≤ 100,000
• ASCII characters
• Single characters must include count 1

Examples

Example 1: Basic Compression

Input: 'aaabbc'

Output: 'a3b2c1'

Explanation: - 'aaa' (3 consecutive a's) → 'a3' - 'bb' (2 consecutive b's) → 'b2' - 'c' (1 c) → 'c1'

Example 2: Empty String

Input: ''

Output: ''

Explanation: - Empty input returns empty output

Example 3: Single Character

Input: 'a'

Output: 'a1'

Explanation: - Single character still includes count

Example 4: No Consecutive Characters

Input: 'abcd'

Output: 'a1b1c1d1'

Explanation: - Each character appears once - All get count 1

Example 5: Long Run

Input: 'aaaaaaaaaa' (10 a's)

Output: 'a10'

Explanation: - 10 consecutive a's compressed to 'a10'

Example 6: Multiple Runs

Input: 'aabbbaabbbbbb'

Output: 'a2b3a2b6'

Explanation: - First run: 'aa' → 'a2' - Second run: 'bbb' → 'b3' - Third run: 'aa' → 'a2' - Fourth run: 'bbbbbb' → 'b6'

Example 7: With Spaces and Punctuation

Input: 'aaa bbb'

Output: 'a3 3b3'

Explanation: - 'aaa' → 'a3' - ' ' (3 spaces) → ' 3' - 'bbb' → 'b3'

What You'll Learn

• Detecting run boundaries in sequences
• Building output strings efficiently
• Two-pointer technique for consecutive elements
• Counting consecutive occurrences
• String concatenation strategies

Why This Matters

Run-length encoding teaches: - Fundamental compression concepts - Pattern recognition in sequences - Efficient iteration techniques - Real-world data processing

This is a common interview question testing string manipulation skills.

Starter Code

def challenge_function(data):
    """
    Perform run-length encoding on string.

    Args:
        data: str to compress

    Returns:
        str: run-length encoded string (format: char + count)
    """
    # Your implementation here
    pass