String Questions at eBay: What to Expect

String manipulation is a core skill for eBay engineers because the platform fundamentally deals with textual data. Product listings, search queries, user messages, payment information, and API payloads are all represented as strings. Efficiently parsing, validating, transforming, and matching this data is critical for search relevance, fraud detection, data normalization, and system performance. The high frequency of string problems in their interview question bank (18 out of 60) reflects this operational reality. Expect questions that test your ability to handle real-world data processing tasks with clean, efficient code.

What to Expect — Types of Problems

eBay's string questions tend to focus on practical application over abstract complexity. You will likely encounter these categories:

1. String Parsing & Validation: Tasks like validating serial numbers, formatting product IDs, or extracting key information from a log line or query string. These test attention to detail and knowledge of built-in string methods.
2. Pattern Matching & Searching: Implementing or using algorithms to find substrings, often related to search functionality. This includes questions on Two-Pointer techniques for palindrome checks or substring searches.
3. String Transformation: Problems requiring you to modify a string according to specific rules, such as URL encoding/decoding, normalizing user input, or implementing basic string compression.
4. HashMap-Based Analysis: A very common pattern. Questions often involve counting character frequencies to determine anagrams, find the first unique character, or compare strings for specific properties.

How to Prepare — Study Tips with One Code Example

Focus on mastering a few key patterns rather than memorizing solutions. Practice writing bug-free code for these fundamentals: iterating over strings, using hash maps for frequency counts, and employing two-pointer techniques. Always clarify edge cases like empty strings, case sensitivity, and whitespace.

A quintessential pattern is using a HashMap (or dictionary) to count character frequencies. This is the foundation for solving anagrams, palindrome permutations, and character difference problems.

def is_anagram(s: str, t: str) -> bool:
    if len(s) != len(t):
        return False

    char_count = {}
    for ch in s:
        char_count[ch] = char_count.get(ch, 0) + 1

    for ch in t:
        if ch not in char_count or char_count[ch] == 0:
            return False
        char_count[ch] -= 1

    return True

Recommended Practice Order

Start with foundational problems to build confidence, then progress to more eBay-relevant scenarios.

1. Core Patterns: First Unique Character in a String, Valid Anagram, Valid Palindrome.
2. Basic Manipulation: String to Integer (atoi), Reverse String, Longest Common Prefix.
3. Advanced Techniques: Longest Substring Without Repeating Characters (Sliding Window), Group Anagrams, Palindromic Substrings.
4. eBay Contextual: Practice problems involving parsing (e.g., log lines, query parameters) and search matching to bridge the gap to domain-specific tasks.

Practice String at eBay