String Questions at Twitter: What to Expect

String manipulation is a core skill for Twitter engineers. The platform handles massive volumes of text data—tweets, usernames, bios, search queries, and real-time content filtering—every second. Efficiently parsing, validating, comparing, and transforming this text is fundamental to performance and scalability. With 13 String-focused problems in their known question pool (out of 53 total), proficiency here is non-negotiable for a successful interview.

What to Expect — Types of Problems

Twitter's String questions typically test your ability to manipulate text while optimizing for time and space. Expect problems in these key areas:

• Two-Pointer & Sliding Window: For finding substrings, palindromes, or sequences without nested loops. Common for "longest substring without repeating characters" or "valid palindrome" variations.
• String Parsing & Simulation: Directly modeling real tasks like parsing a tweet's metadata, validating formats (e.g., usernames), or implementing basic string compression.
• Hash Map for Frequency & Indexing: Used for anagram checks, finding all anagrams in a string, or first unique character problems.
• Interleaving & Dynamic Programming: Less frequent but appears in harder questions involving merging or comparing strings (e.g., edit distance, interleaving strings).

How to Prepare — Study Tips with One Code Example

Focus on patterns, not memorization. Master the two-pointer and sliding window techniques, as they are versatile and frequently applicable. Practice writing clean, edge-case-aware code without built-in shortcuts (like split or reverse for core logic). Always analyze time and space complexity aloud.

A key pattern is the Two-Pointer Palindrome Check. A common question is determining if a string is a valid palindrome, considering only alphanumeric characters and ignoring case.

def is_palindrome(s: str) -> bool:
    left, right = 0, len(s) - 1
    while left < right:
        # Skip non-alphanumeric characters
        while left < right and not s[left].isalnum():
            left += 1
        while left < right and not s[right].isalnum():
            right -= 1
        # Compare characters case-insensitively
        if s[left].lower() != s[right].lower():
            return False
        left += 1
        right -= 1
    return True

Recommended Practice Order

Start with fundamentals and build up to complex combinations.

1. Basic Manipulation: Reverse string, first unique character.
2. Two-Pointer Essentials: Valid palindrome, string compression.
3. Sliding Window: Longest substring without repeating characters.
4. Hash Map Patterns: Valid anagram, group anagrams.
5. Parsing & Simulation: String to integer (atoi), encode/decode strings.
6. Advanced DP/Interleaving: Edit distance (only if time permits).

Practice String at Twitter