Two Pointers Questions at Anduril: What to Expect

Two Pointers is a critical pattern to master for Anduril interviews. With 7 out of their 43 total coding questions dedicated to this technique, it represents a significant portion of their technical assessment. Anduril builds advanced defense technology, which involves processing sensor data, real-time telemetry, and spatial information—domains where efficient array and string manipulation is fundamental. The Two Pointers approach is favored because it provides optimal O(n) solutions with O(1) extra space for many problems involving sorted data or sequences, reflecting the performance-critical nature of their systems engineering.

What to Expect — Types of Problems

Anduril's Two Pointers problems typically fall into three categories. First, opposite-direction pointers are used for problems like finding a pair with a target sum in a sorted array or checking for a palindrome. Second, fast-slow pointers (or runner technique) appear in cycle detection in linked lists or finding a middle element. The third and most common category at Anduril is sliding window, a specialized Two Pointers variant for finding subarrays or substrings that meet a condition, such as the longest substring without repeating characters or a subarray with a maximum sum. Expect problems that test your ability to reduce quadratic brute-force solutions to linear time by intelligently moving pointers based on the problem's constraints.

How to Prepare — Study Tips with One Code Example

Master the pattern by first identifying when to use it: typically for sorted arrays, linked lists, or when a brute-force solution involves nested loops over a sequence. Practice drawing the pointer movements on a whiteboard. Internalize the core logic: initialize pointers, move them based on a condition (often a while loop), and update the result. Always consider edge cases like empty input or pointers going out of bounds.

A fundamental pattern is finding a pair in a sorted array that sums to a target. The brute force is O(n²). The Two Pointers solution starts at both ends, moving the left pointer forward if the sum is too small or the right pointer backward if it's too large.

def two_sum_sorted(numbers, target):
    left, right = 0, len(numbers) - 1
    while left < right:
        current_sum = numbers[left] + numbers[right]
        if current_sum == target:
            return [left + 1, right + 1]  # 1-indexed
        elif current_sum < target:
            left += 1
        else:
            right -= 1
    return [-1, -1]

Recommended Practice Order

Build competency progressively. Start with basic opposite-direction pointer problems (Two Sum II, Valid Palindrome). Move to fast-slow pointer problems (Linked List Cycle, Middle of the Linked List). Then, tackle sliding window problems, beginning with fixed-size windows (Maximum Average Subarray) before advancing to variable-size windows (Longest Substring Without Repeating Characters). Finally, solve Anduril's specific tagged problems to familiarize yourself with their problem style and difficulty level. Time yourself to simulate interview conditions.

Practice Two Pointers at Anduril