Anduril Coding Interview Questions
25 Anduril coding interview problems with full optimal solutions — 8 easy, 12 medium, 5 hard. Every problem ships with multiple approaches (brute-force first, then the optimal), complexity tables for each, company-specific tips on what an Anduril interviewer values, and a FAQ section.
- #1easyfrequently asked
1. Two Sum
Find two indices in an array whose values sum to a target. Anduril uses this as a warm-up to gauge hash-map fluency and whether you can reason about the time-space tradeoff before reaching for the brute-force double loop.
- #3mediumfrequently asked
3. Longest Substring Without Repeating Characters
Find the length of the longest substring with all unique characters. Anduril uses this classic sliding-window problem to test whether you can maintain a dynamic window with O(1)-lookup membership — the same pattern appears in rate-limiting command queues and deduplicating real-time event streams on autonomous platforms.
- #4hardsometimes asked
4. Median of Two Sorted Arrays
Find the median of two sorted arrays in O(log(m+n)) time. Anduril asks this hard problem to test binary-search-on-partition reasoning — the discipline of narrowing an answer space by invariant rather than by exhaustion, a mindset critical when searching configuration spaces in constrained autonomous planning.
- #15mediumfrequently asked
15. 3Sum
Find all unique triplets in an array that sum to zero. Anduril uses this to test whether you can reduce a multi-pointer problem to sorted-array two-pointer reasoning and rigorously eliminate duplicates — the same discipline required when deduplicating redundant sensor readings in a fusion pipeline.
- #20easyfrequently asked
20. Valid Parentheses
Determine if a string of brackets is properly nested and closed. Anduril surfaces this problem in early screens because stack-based state-machine reasoning maps directly to parsing command frames and protocol headers in autonomous systems firmware.
- #21easyfrequently asked
21. Merge Two Sorted Lists
Merge two sorted linked lists into one sorted list. Anduril uses this to test pointer discipline and the ability to reason about invariants — skills that transfer to merging ordered sensor-event streams from multiple autonomous subsystems without breaking temporal ordering.
- #23hardsometimes asked
23. Merge K Sorted Lists
Merge k sorted linked lists into one sorted list efficiently. Anduril asks this hard problem to test whether you can design an O(n log k) solution using a min-heap or divide-and-conquer — skills that translate directly to merging ordered event streams from multiple autonomous subsystems in real time.
- #42hardfrequently asked
42. Trapping Rain Water
Compute how much water can be trapped between elevation bars after a rainfall. Anduril frequently asks this hard problem because it has three distinct approaches at different space tradeoffs — they want to see you enumerate them, pick the O(n)/O(1) two-pointer solution, and explain the invariant rigorously.
- #49mediumsometimes asked
49. Group Anagrams
Cluster a list of strings so that anagrams appear in the same group. Anduril uses this to test hash-map key design — choosing the canonical form of a key is the same challenge as selecting a canonical state representation when deduplicating path-planning states in a search algorithm.
- #53easyfrequently asked
53. Maximum Subarray
Find the contiguous subarray with the largest sum. Anduril uses this to test Kadane's algorithm fluency — a classic greedy-DP technique that mirrors the running-maximum pattern used in signal processing and telemetry anomaly detection on autonomous platforms.
- #56mediumfrequently asked
56. Merge Intervals
Merge all overlapping intervals in a list. Anduril asks this because interval merging is a real problem in mission scheduling and time-window conflict resolution for autonomous systems — you need to sort, then reason carefully about edge cases where intervals share an endpoint.
- #70easysometimes asked
70. Climbing Stairs
Count the number of distinct ways to reach the top of a staircase taking 1 or 2 steps at a time. Anduril asks this to introduce dynamic programming thinking — recognizing that dp[n] = dp[n-1] + dp[n-2] is the same recurrence as Fibonacci, and seeing how memoization converts exponential recursion to linear time.
- #121easysometimes asked
121. Best Time to Buy and Sell Stock
Find the maximum profit from a single buy-sell transaction in a price series. Anduril uses this as a single-pass greedy problem — the same linear scan logic applies to processing time-series sensor streams for anomaly detection in autonomous systems.
- #127hardsometimes asked
127. Word Ladder
Find the shortest transformation sequence from one word to another by changing one letter at a time. Anduril asks this to test BFS shortest-path reasoning on an implicit graph — the ability to model a state-space as a graph and apply BFS for shortest paths is fundamental to route planning and state-space search in autonomous systems.
- #139mediumsometimes asked
139. Word Break
Determine whether a string can be segmented into words from a given dictionary. Anduril uses this DP problem to test whether you can formulate a 1D DP recurrence, recognize subproblem overlap, and choose appropriate memoization — skills that map to parsing structured command protocols with a fixed grammar.
- #146mediumfrequently asked
146. LRU Cache
Design a Least Recently Used cache with O(1) get and put. Anduril frequently asks this because caching is a building block of real-time command pipelines — you need to compose a hash map and a doubly-linked list correctly and articulate why both structures are necessary.
- #200mediumfrequently asked
200. Number of Islands
Count the number of distinct land masses in a binary grid. Anduril asks this because graph traversal on a grid is the foundation of obstacle-map parsing and terrain-segmentation algorithms used in autonomous navigation — engineers need to demonstrate clean BFS/DFS reasoning on 2D state spaces.
- #206easyfrequently asked
206. Reverse Linked List
Reverse a singly linked list in-place. Anduril asks this to verify you can manipulate pointer-based data structures cleanly — a skill that transfers directly to managing sensor-data pipelines and ring-buffer node chains in embedded firmware.
- #207mediumfrequently asked
207. Course Schedule
Determine whether all courses can be completed given their prerequisites — in other words, detect whether a directed graph contains a cycle. Anduril tests this because dependency cycle detection is fundamental to build system safety, firmware task scheduling, and verifying that mission plans are acyclic before execution.
- #215mediumfrequently asked
215. Kth Largest Element in an Array
Find the kth largest element without fully sorting the array. Anduril asks this to see whether you know Quickselect — an O(n) average-time selection algorithm that demonstrates in-place partitioning discipline, the same technique used in real-time ranking systems for sensor-priority queues.
- #238mediumfrequently asked
238. Product of Array Except Self
Compute for each index the product of all other elements without using division. Anduril asks this to verify you can maintain running prefix and suffix state in a single-pass — a technique that appears in sensor-normalization pipelines where you need context from both sides of a measurement without reprocessing the full array.
- #239hardfrequently asked
239. Sliding Window Maximum
Find the maximum value in each sliding window of size k across an array. Anduril asks this hard problem because the monotonic deque pattern — maintaining a decreasing deque of candidates — is a precise data-structure technique that appears in real-time signal processing, where you need the running maximum of a bounded time window without reprocessing old data.
- #322mediumfrequently asked
322. Coin Change
Find the minimum number of coins needed to make up a given amount. Anduril uses this classic 1D DP problem to assess whether you can define the right subproblem, initialize boundary conditions correctly, and reason about infeasible states — the same structured thinking needed when minimizing resource usage in constrained mission planning.
- #347mediumfrequently asked
347. Top K Frequent Elements
Return the k most frequently occurring integers in an array. Anduril asks this to test whether you know the O(n) bucket-sort approach versus the O(n log k) heap — the same frequency-ranking logic drives mission-critical log triage and alert deduplication in real-time systems.
- #704easysometimes asked
704. Binary Search
Search a sorted array for a target value in O(log n) time. Anduril asks this to verify you can implement binary search bug-free — off-by-one errors in loop invariants are a classic source of hard-to-reproduce bugs in firmware, and they watch for them carefully.