String Questions at Coupang: What to Expect

String manipulation is a core skill tested in Coupang's technical interviews. With 15 out of their 53 cataloged questions focused on strings, it's a domain you cannot afford to overlook. For a company built on e-commerce, logistics, and massive data systems, processing text data—from product descriptions and user queries to logistics tracking codes and system logs—is a daily engineering task. Efficient string handling directly impacts search performance, data parsing, and system reliability. Your ability to solve these problems demonstrates practical, applicable coding skill for Coupang's real-world challenges.

What to Expect — Types of Problems

Coupang's string questions tend to focus on applied algorithms rather than trivial manipulation. You can expect problems that test your grasp of fundamental computer science concepts using strings as the medium. Key categories include:

• Two-Pointer & Sliding Window: Extremely common for problems involving palindromes, substrings, or comparisons without extra space. Examples include checking if a string is a palindrome or finding the longest substring without repeating characters.
• Hash Map for Frequency Counting: Essential for anagrams, permutation checks, and character frequency analysis—common when comparing product IDs, tags, or user inputs.
• String Parsing & Simulation: Directly applicable to log parsing, data validation, or interpreting formatted data strings. These test your ability to translate requirements into clean, bug-free code.
• Dynamic Programming on Strings: For more advanced questions, such as calculating edit distance (relevant for search relevance) or counting palindromic substrings.

The problems often combine these patterns, requiring you to implement a core algorithm while handling edge cases inherent to string input.

How to Prepare — Study Tips with One Code Example

Focus on mastering the patterns, not memorizing solutions. Practice by identifying the problem type first, then applying the appropriate technique. Always clarify edge cases: empty strings, case sensitivity, Unicode characters, and allowable characters.

A critical pattern is the Sliding Window for substrings. This is optimal for problems asking for "longest" or "shortest" substrings meeting a condition. The template uses two pointers to represent a window and a hash map to track characters within it.

def length_of_longest_substring(s: str) -> int:
    char_index = {}
    left = 0
    max_len = 0

    for right, ch in enumerate(s):
        # If char is in map and its index is within our current window
        if ch in char_index and char_index[ch] >= left:
            left = char_index[ch] + 1  # Shrink window from the left
        char_index[ch] = right  # Update char's latest index
        max_len = max(max_len, right - left + 1)
    return max_len

Recommended Practice Order

Build competence progressively. Start with basic manipulation and build up to combined patterns.

1. Foundations: Reverse strings, valid parentheses, and basic hash map problems (first unique character, valid anagram).
2. Core Patterns: Practice pure sliding window and two-pointer problems (palindrome, longest substring without repeating characters).
3. Parsing & Simulation: String to integer (atoi), decoding strings, log parsing.
4. Advanced DP: Edit distance, palindromic substrings. Ensure you are comfortable with the core patterns before tackling these.

Consistently write clean, runnable code under time constraints. For Coupang, emphasize efficiency and clarity—your solution should be something you'd approve in a code review.

Practice String at Coupang