String Questions at Anduril: What to Expect

String manipulation is a core skill tested at Anduril. With 10 out of their 43 total coding questions focused on strings, it's a significant portion of their technical interview. This emphasis exists because strings are fundamental to numerous defense and security applications, from parsing sensor data and log files to processing communication protocols and command inputs. Efficiently handling, validating, and transforming textual data is critical in building reliable systems.

What to Expect — Types of Problems

Anduril's string questions are practical and algorithm-focused. You can expect problems that test your ability to manipulate data efficiently and implement clean logic. Common patterns include:

• Parsing and Validation: Tasks like checking for balanced brackets, validating input formats (e.g., serial numbers, commands), or extracting specific substrings from structured data.
• Sliding Window / Two-Pointer Techniques: Finding substrings, anagrams, or the longest substring without repeating characters. These test optimization on sequential data.
• String Transformation: Implementing operations like compression, basic parsing (e.g., atoi), or applying edits.
• Pattern Matching: Simpler versions of matching, often using two-pointer iteration rather than full regex implementation.

The problems are designed to assess both your fundamental coding skill and your attention to edge cases—a must for real-world system code.

How to Prepare — Study Tips with One Code Example

Focus on mastering a few core techniques rather than memorizing problems. Practice implementing solutions from scratch and verbally walking through your logic. Always clarify input assumptions and test with edge cases: empty strings, single characters, very long strings, and strings with special characters.

A key pattern is the Two-Pointer Technique for in-place manipulation or checking palindromes. Here is a classic example: checking 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:
        # Move pointers past non-alphanumeric chars
        while left < right and not s[left].isalnum():
            left += 1
        while left < right and not s[right].isalnum():
            right -= 1
        # Compare characters (case-insensitive)
        if s[left].lower() != s[right].lower():
            return False
        left += 1
        right -= 1
    return True

Recommended Practice Order

Build your skills progressively:

1. Start with fundamental operations: reversal, basic validation, and atoi-style parsing.
2. Master the two-pointer technique for problems like palindromes and substring matching.
3. Practice sliding window algorithms for finding substrings with specific constraints.
4. Tackle parsing problems that involve state, like bracket validation or simple tokenization.
5. Combine patterns, such as using a hash map with a sliding window for anagram problems.

This order ensures you build on core concepts before handling more complex combinations.

Practice String at Anduril