String Questions at Yelp: What to Expect

String manipulation is a core skill for software engineers at Yelp. The platform relies heavily on processing and analyzing user-generated text—from reviews and business descriptions to search queries and location data. Efficiently parsing, validating, searching, and transforming these strings is critical for features like search relevance, spam detection, and data normalization. With 17 out of 27 of Yelp's tagged coding problems being String-based, mastering this domain is non-negotiable for your interview.

What to Expect — Types of Problems

Yelp's String questions typically focus on practical, real-world text processing. You won't find abstract, purely mathematical string puzzles. Instead, expect problems that mirror the company's engineering needs.

• String Parsing and Validation: Tasks like checking if a review meets formatting guidelines, validating phone numbers or addresses, or extracting specific information from a block of text.
• Pattern Matching and Searching: Implementing or utilizing algorithms to find substrings, such as checking for keywords in a business description or detecting duplicate content. This often involves sliding window techniques or KMP (Knuth-Morris-Pratt) for efficiency.
• String Transformation and Encoding: Problems like compressing strings, implementing a basic URL encoder, or reformatting text data from one standard to another.
• Hash Map and Frequency Analysis: A very common pattern. Many problems reduce to counting character or word frequencies to determine anagrams, find the most common review word, or identify unique characters.

How to Prepare — Study Tips with One Code Example

Focus on the fundamentals. Ensure you are fluent in your language's string API (methods for split, join, substring, indexOf, etc.). The most critical mental model is to treat strings as arrays of characters. This unlocks array-based techniques like two-pointers and sliding windows.

The single most important pattern is using a Hash Map (Dictionary or Object) to track character frequencies. This is the cornerstone for solving anagrams, palindromes, and substring problems.

def is_anagram(s: str, t: str) -> bool:
    if len(s) != len(t):
        return False
    char_count = {}
    for char in s:
        char_count[char] = char_count.get(char, 0) + 1
    for char in t:
        if char not in char_count or char_count[char] == 0:
            return False
        char_count[char] -= 1
    return True

Recommended Practice Order

1. Frequency & Hash Map: Start with anagram and palindrome problems to internalize the frequency-counting pattern.
2. Two-Pointers: Practice in-place string reversal and checking for palindromes. This builds intuition for character-by-character processing.
3. Sliding Window: Move on to finding substrings with specific properties (e.g., longest substring without repeating characters). This is a natural extension of two-pointers and hash maps.
4. Parsing & Simulation: Finally, tackle multi-step parsing problems. These test your ability to break down a problem, handle edge cases, and write clean, bug-free code under time constraints.

Practice String at Yelp