Navigating the competitive landscape of tech interviews, especially at a company like Airbnb, requires meticulous preparation. Airbnb's reputation for high-quality engineering means its coding interviews are rigorous, focusing on your problem-solving abilities, algorithmic knowledge, and data structure mastery. Success hinges on more than just knowing solutions; it's about demonstrating your thought process, handling edge cases, and writing clean, efficient code. This comprehensive guide will equip you with insights into the most common types of questions encountered, providing structured approaches to tackle them confidently and showcase your technical prowess to potential employers. Preparing effectively involves understanding the "why" behind these questions and developing a strategic mindset for optimal performance.
What Are Airbnb Coding Interview Questions?
Airbnb coding interview questions are primarily designed to assess a candidate's proficiency in data structures and algorithms. These challenges often range from medium to hard difficulty, mirroring the complexity of problems found on platforms like LeetCode or HackerRank. Interviewers look for candidates who can not only produce a correct solution but also articulate their thought process, discuss time and space complexity, and handle various edge cases. The types of questions span fundamental areas such as arrays, strings, hash maps, stacks, queues, trees, and graphs. Beyond theoretical knowledge, they often test your ability to translate abstract problem statements into executable code, reflecting real-world software engineering challenges at scale.
Why Do Interviewers Ask Airbnb Coding Interview Questions?
Interviewers at Airbnb ask coding questions to evaluate several critical competencies essential for a successful software engineering role. Firstly, they assess your foundational knowledge of data structures and algorithms, which are the building blocks for efficient and scalable systems. Secondly, these questions reveal your problem-solving methodology, including how you break down complex problems, identify patterns, and devise optimal solutions. Thirdly, they gauge your coding proficiency, clarity, and ability to write clean, maintainable code. Lastly, coding interviews provide insight into your communication skills—how effectively you can explain your logic, discuss trade-offs, and respond to feedback. This holistic assessment helps Airbnb identify candidates who can contribute effectively to their innovative and fast-paced engineering environment.
How do you find all unique triplets in an array that sum to zero?
What is the length of the longest substring without repeating characters?
How do you find two numbers in an array that add up to a specific target?
How do you group anagrams together from a list of strings?
Given an integer, how do you find the maximum steps following the Collatz Conjecture rules?
How would you design a Least Recently Used (LRU) cache system?
How do you detect if a linked list contains a cycle?
What is the maximum contiguous subarray sum in a given array?
How would you implement a stack with an additional method to get the minimum element?
How do you reverse a linked list?
How do you merge k sorted linked lists into one sorted list?
How do you find the maximum depth of a binary tree?
How would you clone a graph?
How do you validate if a given binary tree is a binary search tree?
How do you find the minimum window substring in one string that contains all characters of another?
How do you find the shortest path from one cell to another in a grid?
What is the minimum number of coins needed to make change for a given amount?
What is the maximum sum of a submatrix in a 2D matrix?
How do you find the next greater element for each element in an array?
Given courses and prerequisites, how do you check if a valid schedule can be created?
How would you implement a Trie (Prefix Tree) for efficient word searching?
How do you determine if a string can be segmented into a space-separated sequence of dictionary words?
How do you find the Kth largest element in an unsorted array?
How would you serialize and deserialize a binary tree?
Given n non-negative integers, how do you find two lines that form a container with the most water?
How do you determine if an input string of parentheses is valid?
Given n non-negative integers representing an elevation map, how much water can be trapped after raining?
How do you generate all possible subsets (the power set) of an integer array?
How do you compute an array where each element is the product of all elements except itself?
How do you find the lowest common ancestor (LCA) of two nodes in a binary tree?
Preview List
1. How do you find all unique triplets in an array that sum to zero?
Why you might get asked this:
This question tests your ability to handle array manipulation, sorting, and the two-pointer technique efficiently, along with managing duplicate results.
How to answer:
Sort the array. Iterate through each element, then use two pointers (left and right) on the remaining array to find pairs that sum to the negative of the current element. Skip duplicates.
Example answer:
First, sort the array to efficiently manage order and duplicates. Iterate with a main pointer i. For each nums[i], use two pointers, left and right, starting at i+1 and n-1 respectively. Move left and right inward based on the sum, skipping duplicates at each step to ensure unique triplets.
2. What is the length of the longest substring without repeating characters?
Why you might get asked this:
This assesses your understanding of string manipulation, hash maps (or sets), and the sliding window technique for optimal performance.
How to answer:
Use a sliding window approach with a hash map (or set) to store characters encountered within the current window. Expand the window while characters are unique, and shrink it from the left when a duplicate is found.
Example answer:
Employ a sliding window defined by two pointers, left and right. Maintain a set to store characters within the current window. As right advances, add s[right] to the set. If s[right] is already in the set, move left forward and remove s[left] from the set until the window is valid again. Update maximum length.
3. How do you find two numbers in an array that add up to a specific target?
Why you might get asked this:
A fundamental question testing hash map usage for quick lookups and basic array traversal, often a warm-up for more complex problems.
How to answer:
Iterate through the array. For each number, calculate the complement needed to reach the target. Check if this complement exists in a hash map. If not, add the current number and its index to the map.
Example answer:
Use a hash map to store numbers and their indices. For each number num in the array, calculate complement = target - num. Check if complement exists as a key in the map. If it does, return [map[complement], currentindex]. Otherwise, add num and its currentindex to the map.
4. How do you group anagrams together from a list of strings?
Why you might get asked this:
This tests your ability to use hash maps with custom keys, often involving string manipulation (sorting characters) to identify groups.
How to answer:
Create a hash map where the key is the sorted version of a word (e.g., "eat" -> "aet") and the value is a list of original words that are anagrams. Iterate through the input strings, sort each, and add the original to the corresponding list in the map.
Example answer:
Initialize a hash map. Iterate through each string s in the input list. Convert s to a character array, sort it, and convert it back to a string; this sorted string acts as the key. Append the original string s to the list associated with this key in the hash map. Finally, return all values (lists of anagrams) from the map.
5. Given an integer, how do you find the maximum steps following the Collatz Conjecture rules?
Why you might get asked this:
This problem explores iterative processes, basic conditional logic, and potentially memoization for optimization if asked for a range.
How to answer:
Implement a loop that applies the Collatz rules: if n is even, n = n / 2; if n is odd, n = 3 * n + 1. Count the steps until n becomes 1. This directly computes for a single n.
Example answer:
Initialize a steps counter to zero. While n is not 1, increment steps. If n is even, update n = n / 2. If n is odd, update n = 3 * n + 1. Return steps. For a range of numbers, compute steps for each and find the maximum.
6. How would you design a Least Recently Used (LRU) cache system?
Why you might get asked this:
A classic system design question that evaluates your knowledge of data structures (hash maps and doubly linked lists) and handling time/space constraints.
How to answer:
Combine a hash map for O(1) key lookups and a doubly linked list to maintain item order (recency). The map stores key -> node, and the list tracks usage, with most recent at head and least recent at tail.
Example answer:
Implement get and put methods. Use a HashMap for O(1) access to nodes and a DoublyLinkedList for maintaining recency. get moves accessed node to head. put adds new node to head; if capacity exceeded, remove tail node.
7. How do you detect if a linked list contains a cycle?
Why you might get asked this:
Tests your understanding of linked list traversal and the two-pointer technique (Floyd's Cycle-Finding Algorithm).
How to answer:
Use two pointers, slow and fast. slow moves one step at a time, fast moves two steps. If there's a cycle, they will eventually meet. If fast reaches null, there's no cycle.
Example answer:
Initialize slow = head and fast = head. Loop while fast and fast.next are not null. Move slow = slow.next and fast = fast.next.next. If slow and fast meet, a cycle exists, return true. If the loop finishes, return false.
8. What is the maximum contiguous subarray sum in a given array?
Why you might get asked this:
This is a standard dynamic programming problem (Kadane's algorithm), testing your ability to optimize solutions for contiguous ranges.
How to answer:
Use Kadane's algorithm. Maintain two variables: currentmax for the maximum sum ending at the current position, and globalmax for the overall maximum sum found so far.
Example answer:
Initialize maxsofar = nums[0] and currentmax = nums[0]. Iterate from the second element: currentmax = max(nums[i], currentmax + nums[i]). maxsofar = max(maxsofar, currentmax). This ensures currentmax is always the maximum sum ending at the current index, and maxso_far tracks the global maximum.
9. How would you implement a stack with an additional method to get the minimum element?
Why you might get asked this:
Tests data structure design and efficient retrieval of minimums while maintaining stack properties (LIFO).
How to answer:
Use two stacks: one for regular elements and another for tracking minimums. When pushing, if the new element is less than or equal to the current minimum, push it onto the min stack. When popping, if the popped element is the current minimum, pop from the min stack too.
Example answer:
Maintain a primary stack for all elements. For min functionality, use a separate minstack. When push(x), if x <= minstack.peek(), push x to minstack. When pop(), if poppedelement == minstack.peek(), pop from minstack. getMin() returns min_stack.peek().
10. How do you reverse a linked list?
Why you might get asked this:
A foundational linked list problem that assesses pointer manipulation and iterative/recursive thinking.
How to answer:
Use an iterative approach with three pointers: prev (initially null), current (initially head), and next_node. In each step, reverse the current node's pointer, then advance all three pointers.
Example answer:
Initialize prev = null, curr = head. Iterate while curr is not null: store curr.next in nexttemp, set curr.next = prev, update prev = curr, then set curr = nexttemp. Return prev as the new head.
11. How do you merge k sorted linked lists into one sorted list?
Why you might get asked this:
This problem evaluates your ability to handle multiple data streams and utilize priority queues (min-heap) for efficient merging.
How to answer:
Use a min-priority queue. Add the head of each linked list to the priority queue. Repeatedly extract the minimum node, add it to the merged list, and then add its next node to the priority queue until empty.
Example answer:
Create a min-priority queue and add the first node of each list into it. Initialize a dummy head for the merged list. While the priority queue is not empty, extract the smallest node. Append it to the merged list and, if it has a next node, add that next node to the priority queue.
12. How do you find the maximum depth of a binary tree?
Why you might get asked this:
A common tree traversal question, testing your understanding of recursion or iterative BFS/DFS for tree properties.
How to answer:
Use a recursive Depth-First Search (DFS) approach. The depth of a node is 1 plus the maximum depth of its left or right subtree. The base case is a null node (depth 0).
Example answer:
If root is null, return 0. Otherwise, recursively calculate leftdepth = maxDepth(root.left) and rightdepth = maxDepth(root.right). The maximum depth for the current node is 1 + max(leftdepth, rightdepth).
13. How would you clone a graph?
Why you might get asked this:
Tests graph traversal (BFS/DFS) and managing visited nodes, along with creating new nodes and edges to build an identical copy.
How to answer:
Use BFS or DFS along with a hash map. The map stores mappings from original nodes to their cloned counterparts. During traversal, if a node hasn't been cloned, create a new one and store the mapping. Then, clone its neighbors.
Example answer:
Initialize a HashMap to store original-to-cloned node mappings. Use BFS: add the starting node to a queue and clone it. While the queue is not empty, dequeue a node, iterate its neighbors. For each neighbor, if not cloned, clone it and add to queue. Connect cloned neighbors.
14. How do you validate if a given binary tree is a binary search tree?
Why you might get asked this:
Assesses understanding of BST properties and recursive traversal with range checks.
How to answer:
Use an in-order traversal, ensuring each node's value is greater than the previous one visited. Alternatively, use a recursive DFS approach passing min and max bounds for each subtree.
Example answer:
Implement a helper function isValidBST(node, minVal, maxVal). If node is null, return true. Check node.val > minVal AND node.val < maxVal. Recursively call isValidBST(node.left, minVal, node.val) and isValidBST(node.right, node.val, maxVal). Initial call: isValidBST(root, -infinity, +infinity).
15. How do you find the minimum window substring in one string that contains all characters of another?
Why you might get asked this:
A challenging sliding window problem requiring precise tracking of character counts using hash maps.
How to answer:
Use a sliding window. Maintain two hash maps: one for character counts in the target string t, and another for character counts in the current window of s. Expand the window, updating counts. When all characters of t are covered, shrink from the left to find the minimum valid window.
Example answer:
Pre-process t into a charcountst map. Use a windowcounts map for s. Expand the right pointer; if s[right] is in t, update windowcounts and increment a matchedchars counter. When matchedchars equals t's unique chars, contract the left pointer, updating minimum length, until t is no longer covered.
16. How do you find the shortest path from one cell to another in a grid?
Why you might get asked this:
Tests graph traversal (specifically Breadth-First Search or BFS), which is ideal for shortest path on unweighted graphs.
How to answer:
Use Breadth-First Search (BFS). Start from the source, explore neighbors layer by layer, marking visited cells and storing distances. The first time the destination is reached, the path found is the shortest.
Example answer:
Initialize a queue with the starting cell and its distance (0). Use a visited set to avoid cycles. While the queue is not empty, dequeue a cell. If it's the target, return its distance. Otherwise, enqueue all unvisited, valid neighbors with distance + 1.
17. What is the minimum number of coins needed to make change for a given amount?
Why you might get asked this:
A classic dynamic programming problem that requires building up solutions from smaller subproblems.
How to answer:
Use dynamic programming. Create a DP array dp where dp[i] is the minimum coins to make amount i. Initialize dp[0] = 0 and others to infinity. Iterate from 1 to amount, and for each amount i, consider each coin c in coins. If i - c >= 0, dp[i] = min(dp[i], 1 + dp[i - c]).
Example answer:
Create dp array of size amount+1, initialized to infinity, dp[0]=0. For each coin in coins: For each i from coin to amount: dp[i] = min(dp[i], 1 + dp[i - coin]). Return dp[amount] if not infinity, else -1.
18. What is the maximum sum of a submatrix in a 2D matrix?
Why you might get asked this:
This extends Kadane's algorithm to 2D, requiring nested loops and clever application of 1D maximum subarray sum.
How to answer:
Iterate over all possible pairs of column boundaries (left and right). For each pair, sum up elements within those columns row by row to create a 1D array. Apply Kadane's algorithm to this 1D array to find the maximum sum.
Example answer:
Iterate leftcol from 0 to C-1. Iterate rightcol from leftcol to C-1. For each pair, create a rowsum array by summing matrix[row][col] for col from leftcol to rightcol. Apply Kadane's algorithm to row_sum to find the maximum sum for this submatrix band. Track the overall maximum.
19. How do you find the next greater element for each element in an array?
Why you might get asked this:
Tests stack usage for maintaining order and efficiently finding the next greater element in a single pass.
How to answer:
Use a monotonic stack. Iterate through the array. For each element, pop elements from the stack that are smaller than the current element, setting their next greater element to the current one. Push the current element onto the stack.
Example answer:
Initialize an empty stack and a result array. Iterate through the input array from right to left. While the stack is not empty and the top of the stack is less than or equal to the current element, pop from the stack. If the stack is empty, the next greater element is -1; otherwise, it's the stack's top. Push the current element onto the stack.
20. Given courses and prerequisites, how do you check if a valid schedule can be created?
Why you might get asked this:
This is a graph problem, typically solved with topological sorting using DFS or BFS, assessing cycle detection.
How to answer:
Model courses and prerequisites as a directed graph where an edge u -> v means u is a prerequisite for v. Use topological sort (BFS with in-degrees or DFS with cycle detection). If a cycle exists, no valid schedule can be created.
Example answer:
Build an adjacency list for the graph and an indegree array for each course. Initialize a queue with all courses having indegree 0. While the queue is not empty, dequeue a course, decrement indegree of its neighbors. If a neighbor's indegree becomes 0, enqueue it. If the number of processed courses equals total courses, a valid schedule exists.
21. How would you implement a Trie (Prefix Tree) for efficient word searching?
Why you might get asked this:
Tests your ability to design a custom data structure optimized for string operations like prefix matching and searching.
How to answer:
A Trie consists of nodes, where each node represents a character. Each node has children representing subsequent characters. A boolean flag marks if a node completes a word. Implement insert, search, and startsWith.
Example answer:
Define a TrieNode class with a HashMap children and a boolean isEndOfWord. The Trie class has a root node. insert traverses, creating nodes as needed. search and startsWith traverse the trie to find the path, checking isEndOfWord for search.
22. How do you determine if a string can be segmented into a space-separated sequence of dictionary words?
Why you might get asked this:
A classic dynamic programming problem, or sometimes solvable with recursion with memoization, exploring string partitioning.
How to answer:
Use dynamic programming. Create a boolean array dp where dp[i] is true if s[0...i-1] can be segmented. dp[i] is true if dp[j] is true AND s[j...i-1] is in the dictionary for some j < i.
Example answer:
Initialize dp array of size n+1 with false, dp[0]=true. Iterate i from 1 to n. For each i, iterate j from 0 to i-1. If dp[j] is true and the substring s.substring(j, i) is in the wordDict (use a HashSet for O(1) lookup), set dp[i]=true and break the inner loop. Return dp[n].
23. How do you find the Kth largest element in an unsorted array?
Why you might get asked this:
Tests sorting algorithms, partition schemes (QuickSelect), or heap usage for efficient selection.
How to answer:
The most efficient approach is QuickSelect (a variant of QuickSort), which has an average time complexity of O(N). Alternatively, use a min-heap of size K: iterate through elements, if current is larger than heap's min, pop min and push current.
Example answer:
Use a min-priority queue (min-heap). Iterate through the array elements. Add each element to the heap. If the heap's size exceeds k, remove the smallest element (heap's root). After iterating through all elements, the kth largest element will be the root of the heap.
24. How would you serialize and deserialize a binary tree?
Why you might get asked this:
A design problem requiring careful tree traversal (BFS or DFS) to flatten it into a string and reconstruct it reliably.
How to answer:
For serialization, perform a BFS (level-order traversal) or DFS (pre-order, in-order, or post-order) and store node values in a string, using a special marker for null nodes (e.g., "#"). For deserialization, parse the string to reconstruct the tree structure.
Example answer:
Use BFS for serialization: append node values (or "null" for null nodes) to a string, separated by delimiters. For deserialization: parse the string into a list of values. Use a queue to build the tree level by level, linking parent nodes to children as per the parsed values.
25. Given n non-negative integers, how do you find two lines that form a container with the most water?
Why you might get asked this:
A greedy algorithm problem usually solved with the two-pointer technique to optimize area calculation.
How to answer:
Use two pointers, left and right, starting at the ends of the array. Calculate the area formed by min(height[left], height[right]) * (right - left). Move the pointer pointing to the shorter line inward to potentially find a taller line.
Example answer:
Initialize left = 0, right = n-1, maxarea = 0. While left < right: calculate currentarea = min(height[left], height[right]) * (right - left). Update maxarea = max(maxarea, currentarea). If height[left] < height[right], increment left. Else, decrement right. Return maxarea.
26. How do you determine if an input string of parentheses is valid?
Why you might get asked this:
A classic stack problem testing your ability to match opening and closing brackets correctly.
How to answer:
Use a stack. Iterate through the string: if an opening bracket, push to stack. If a closing bracket, check if stack is empty or its top is not the matching opening bracket; if so, invalid. Else, pop. At the end, stack must be empty.
Example answer:
Initialize an empty stack and a map for bracket pairs ({'(', ')'}, etc.). Iterate string s. If char is opening, push to stack. If char is closing, check if stack is empty or stack.pop() doesn't match; return false. After loop, return stack.isEmpty().
27. Given n non-negative integers representing an elevation map, how much water can be trapped after raining?
Why you might get asked this:
A challenging array problem often solved using two pointers or dynamic programming to find bounding walls for water.
How to answer:
Use two pointers, left and right, starting at the ends. Maintain leftmax and rightmax. If height[left] < height[right], water is determined by leftmax. Add leftmax - height[left] to total and increment left. Else, do same for right.
Example answer:
Initialize left = 0, right = n-1, totalwater = 0, leftmax = 0, rightmax = 0. While left <= right: If leftmax <= rightmax, update leftmax = max(leftmax, height[left]), totalwater += leftmax - height[left], left++. Else, update rightmax = max(rightmax, height[right]), totalwater += right_max - height[right], right--.
28. How do you generate all possible subsets (the power set) of an integer array?
Why you might get asked this:
A common backtracking or bit manipulation problem testing combinatorial generation.
How to answer:
Use recursion with backtracking: For each element, decide to include it or not. Or, use an iterative approach treating each subset as a binary number where each bit indicates element presence.
Example answer:
Implement a recursive backtrack function taking currentsubset, startindex. Add currentsubset to result list. Loop i from startindex to n-1. Add nums[i] to currentsubset, recursively call backtrack(currentsubset, i + 1), then remove nums[i] (backtrack step).
29. How do you compute an array where each element is the product of all elements except itself?
Why you might get asked this:
Tests array manipulation, often requiring a solution without division and in O(N) time, typically involving prefix and suffix products.
How to answer:
Compute two arrays: prefixproducts (product of elements to the left) and suffixproducts (product of elements to the right). The result at index i is prefixproducts[i-1] * suffixproducts[i+1]. Handle edge cases for first/last elements.
Example answer:
Create result array. First pass: calculate prefix products. result[0] = 1, result[i] = result[i-1] nums[i-1]. Second pass (from right to left): maintain a suffix_product variable, multiply result[i] by suffix_product, then update suffix_product = nums[i].
30. How do you find the lowest common ancestor (LCA) of two nodes in a binary tree?
Why you might get asked this:
A common tree problem testing recursive traversal and understanding of tree structure and parent-child relationships.
How to answer:
Use a recursive approach. If the current node is p or q, return it. Recursively search left and right subtrees. If both return non-null, current node is LCA. If only one returns non-null, that is the LCA.
Example answer:
Define findLCA(node, p, q): If node is null, p, or q, return node. Recursively call left = findLCA(node.left, p, q) and right = findLCA(node.right, p, q). If both left and right are non-null, node is the LCA. If only one is non-null, return that one.
Other Tips to Prepare for an Airbnb Coding Interview
Beyond practicing specific problems, a holistic approach to interview preparation is crucial for Airbnb. Firstly, internalize the core concepts of data structures and algorithms. Don't just memorize solutions; understand the underlying principles and when to apply them. As the famous computer scientist Donald Knuth once said, "Premature optimization is the root of all evil," but understanding complexity and choosing efficient algorithms is key. Secondly, cultivate strong communication skills. Interviewers want to see how you think, debug, and explain your solutions. Articulate your thought process, clarify assumptions, and discuss trade-offs explicitly.
Thirdly, practice mock interviews extensively. Tools like Verve AI Interview Copilot can be incredibly beneficial here. It provides real-time feedback on your code, explanations, and even helps identify areas for improvement in your communication style. Verve AI Interview Copilot offers a realistic interview environment, allowing you to simulate the pressure and build confidence. Leverage its features to refine your approach to each question. "The only way to do great work is to love what you do," and preparing thoroughly shows your dedication. Remember to consider edge cases and constraints, and always test your code. For comprehensive practice, explore resources like Verve AI Interview Copilot to simulate real interview conditions. Find out more at https://vervecopilot.com.
Frequently Asked Questions
Q1: How much LeetCode should I do for an Airbnb interview?
A1: Focus on medium to hard problems. Aim for at least 100-150 problems, emphasizing common patterns like two pointers, sliding window, BFS/DFS, and dynamic programming.
Q2: What programming language is best for Airbnb coding interviews?
A2: Python, Java, JavaScript, and C++ are common. Choose the language you are most proficient and comfortable with, as clarity and efficiency matter most.
Q3: Should I also prepare for system design questions?
A3: For software engineer roles, especially mid-level and senior, system design is a crucial component. Juniors may have lighter or no system design questions.
Q4: How important is Big O notation in Airbnb interviews?
A4: Extremely important. You must be able to analyze and discuss the time and space complexity of your solutions for optimal performance.
Q5: What if I get stuck during the interview?
A5: Communicate your thought process. Explain your current approach, what's blocking you, and what alternatives you're considering. Don't hesitate to ask for hints.
