Facebook Coding Interview Questions to Nail Your Next Interview

Facebook has one of the most challenging interview processes compared to other FAANG companies. The interview tests your core problem-solving and analytical skills, your ability to work with large-scale distributed systems, and your behavioral tendencies.

Cracking Facebook’s technical interview requires a sound prep strategy that addresses various elements that influence interview success. Facebook doesn’t hire engineers merely based on a strong academic record. Candidates go through several rounds of rigorous evaluation before they’re made an offer.

In this article, we’ll look at common coding interview questions asked at Facebook. Here is what this article will cover:

• The Facebook interview process
• What is expected of candidates in Facebook’s interview?
• Topics to prepare for Facebook's coding interview
• Facebook coding interview questions

The Facebook Interview Process

Facebook’s interview process comprises three main rounds of interviews:

1. The Technical Phone Screen Interview: The technical phone screen is a screening round to filter candidates based on their proficiency in the programming language of their choice and their ability to solve coding problems around algorithms and data structures.
2. The On-site Interview: The on-site interview typically consists of 3-4 rounds where hiring managers evaluate your problem-solving and analytical skills. Your knowledge and ability to solve tricky coding problems by employing advanced concepts in DS and algorithms are extensively evaluated.
3. The Behavioral Interview: Behavioral interviews are essentially held to help hiring managers understand what attributes candidates will display in workplace-related situations. Behavioral interviews are given more weightage for upper management and technical lead interviews at FAANG.

While these are the main rounds that take place in Facebook’s coding interview, the interview rounds may differ based on the position you’re applying to.

Want to learn more about the Facebook interview process? Click here.

What Is Expected of Candidates in Facebook’s Coding Interview?

Facebook looks for specific traits in programmers while making a hiring decision. If you wish to land an offer from Facebook, here are some aspects that you must display during the interview:

Proficiency in your programming language: Being adept with the programming language of your choice is a fundamental requirement. You should be able to apply advanced concepts to code up algorithms. Programming language proficiency is important in the technical phone screen as well as the on-site interview.

Understanding the problem: The second thing that recruiters look at is how well you analyze the problem. Are you going back and forth too many times? Are you asking the right questions? These are things hiring managers closely look at during your interview.

Your ability to articulate: It is often advised to think out your solutions aloud to give the interviewer a window into your thoughts. Recruiters don’t look at how quickly you solve a problem or how many shots you took at it. They want candidates to ask the right questions and look at solutions from multiple angles to arrive at the most optimal one.

Correcting your mistakes: Hiring managers expect that you correct your mistakes while going about solving the problem. They expect that you recognize faults without being nudged.

Writing code on a whiteboard: Whiteboard coding is another important element that recruiters look at. Coding on a whiteboard exposes your inadequacies, if there are any. Striking off code multiple times without thinking it through isn’t what recruiters look for in candidates. Practicing whiteboard coding is important, especially for the on-site interview.

Topics to Prepare for Facebook Coding Interviews

Your knowledge of core data structures and algorithms must be in-depth if you want to stand a chance at acing Facebook’s coding interview. Below is the list of topics to prepare for Facebook’s coding interview:

• Arrays, strings, and linked lists
• Sorting algorithms — quicksort, merge sort, heap sort, etc.
• Hash tables and queues
• Recursion
• Trees and graphs
• Graph algorithms, including greedy algorithms
• Dynamic programming

Facebook Coding Interview Questions

As an aspiring Facebooker, here are some common Facebook coding interview questions you can expect:

1. For a given string, “S,” write a function to compute the length of the longest substring that has only distinct characters.
   (Click here for the solution)
2. Write a code to reverse the elements in a given Linked List “L.”
   (Click here for the solution)
3. Given K sorted arrays arr, of size N each, merge them into a new sorted array.
   (Click here for the solution)
4. You’re given a binary tree T. Write a function to determine if the given tree is a Binary Search Tree or not.
   (Click here for the solution)
5. Given two sorted arrays (non-descending order), return a new array containing elements that are present in both input arrays (the intersection of arrays).
   (Click here for the solution)

More practice Facebook coding interview problems:

1. You’re given a set of integers. Write a bash script to convert the given set of integers into their corresponding roman numerals.
2. For a given array of integers in a sequence, write a code to determine the missing element in the sequence.
3. For a given unsorted array comprising non-negative integers, write a function to find the contiguous subarray that returns the sum of non-negative integers in the array.
4. You’re given two arrays that are sorted and of varying sizes. Write a code to merge the two arrays such that elements in the merged array appear in increasing order.
5. For a given Linked List “L,” write a function to pick a random node from the Linked List.
6. For a given array of n positive integers, write a function to determine the inversion count of the array.
7. For a given Binary Tree T, write a function to print only the left view of the tree.
8. You’re given a Binary Tree T. Write a code to print the height of the Binary Tree.
9. For a given Binary Tree, write a function to connect the nodes of the Binary Tree that are at the same level.
10. You’re given a binary search tree with unique values; two node values are given. Write a function to find the lowest common ancestors of the two nodes.
11. You’re given a Binary Tree. Write a code to convert it to a Doubly Linked List (DLL) In-Place. The left and right pointers in the nodes are to be used as previous and next pointers, respectively, in the converted DLL.
12. Write a code to count the leaves in a given Binary Search Tree BT.
13. Write a code to implement the Serialize and Deserialize functions on a given binary search tree.
14. Given an array of integers, write a program to return the next greater element for each element in the array. The array comprises all distinct numbers. If there doesn’t exist a greater element to the right of a given element, the value returned in that position should be -1.
15. Write a program to implement a Queue using two stacks.
16. For a given set of 2 sorted arrays, “X” and “Y” with respective sizes “n” and “m,” write a code to merge the two sorted arrays such that their characters appear in decreasing order.
17. For a given set of 2 arrays “X” and “Y” consisting of positive integers, write a code to find the total no. of pairs to satisfy the condition x^y>y^x, where “x” is an element of array “X” and “y” is an element of array “Y.”
18. For a given array, “K,” where all the elements in the array are distinct, write a function to find the Kth smallest element where “K” is a number and is smaller than the array’s size.
19. You’re given an array “X” of size “N,” containing sets of 0s, 1s, and 2s. Write a program to sort the array elements in ascending order.
20. For a given array “X” of N positive integers, write a function to return the value “True” if a particular triplet (a,b,c) accurately satisfies the condition: a^2+b^2=c^2 (this is commonly called the Pythagorean Triplet problem).
21. You’re given two Linked Lists, “A” and “B,” that are sorted. Write a code to merge the two Linked Lists.
22. Explain Longest Common Sequence and Longest Increasing Subsequence in dynamic programming.
23. For a given Singly Linked List “K,” write a code to select a particular “random” node from the list.
24. Explain the process to implement BFS and DFS in a given graph.
25. Explain how to implement the functions “strstr” and “Atoi” by citing examples.
26. Write a code to find the middle element in a given Linked List “K.”
27. Write a program function to implement Loop Detection and Loop Removal in a given Linked List “K.”
28. For a given string, “K,” write a function to eliminate duplicates from the string.
29. Write a program to determine if two given strings, “A” and “B,” of set sizes are anagrams of each other.
30. For a given Binary Tree, write a function to print the bottom view of the tree from left to right.
31. For a given Binary Tree (BT), write a code to print the vertical traversal from the leftmost to rightmost levels.
32. Explain a few Greedy Algorithms and their applications.
33. Write a code to find the longest path in a given matrix m*n, where all the values in the matrix are unique. The path should be such that the cells should appear in ascending order.
34. Find maximum path sum in a non-empty binary tree.
35. Rotate a given matrix.
36. Given a binary search tree, BST, convert it into a sorted circular doubly linked list.
37. Given a tree, find the largest distance between two nodes of the tree.

Want to practice more coding problems? Click here for coding interview problems with solutions.

How to Prepare for Facebook’s Coding Interview

In order to crack Facebook’s coding interview, the right strategy needs to be in place. Here’s what you need to do to ace Facebook’s technical rounds:

Practice a Good Number of Problems

Create a solid schedule that involves practicing at least 1-2 problems every day. Ideally, you must do this for at least 10-12 weeks before your interview. Practicing enough problems will expose you to different patterns, allowing you to apply patterns to solve tougher and more tricky problems. Rain or shine, make sure you remain consistent with your schedule.

In the weeks leading up to your interview, practice at least 150 problems as a thumb rule. This will broaden your exposure and help you tackle challenging and tricky problems at your interview. More so, it will help you look at problems from multiple solution perspectives, thereby helping you find optimal solutions to interview problems more easily.

Related article: “Why FAANG Companies Test for Problem Solving Skills in Their Interviews”

Give Yourself Adequate Time to Prepare

A lot of candidates ignore this crucial component and jump into the interview a tad early. Giving yourself enough time to prepare is extremely important, given that these interviews aren’t that easy and the competition is particularly stiff and unforgiving.  

Pick a Programming Language That You’re Good At

You may be well-versed with multiple programming languages. But for the interview, make sure you pick one that you’re especially good with and understand the nuances of. Besides evaluating you in concepts around core DS and algorithms, hiring managers also look at how proficient you are with the programming language of your choice. This happens in the technical phone screen as well as the on-site interviews.

Related article: “Most Popular Coding Languages for FAANG Interviews in 2021”

Solve Tough Problems Multiple Times

Revision is key to mastering concepts, especially programming concepts. In the case of tough and tricky problems, going through the solution multiple times is a must. This way, inherent patterns in problems will be etched in your memory, allowing you to confront challenging and complex questions in the interview.

Practice Mock Interviews

Practicing mock interviews is the best way to know where you stand. However, they must be practiced with the right individuals. Interview Kickstart offers a mock interview program where you get to practice mock interviews with hiring managers and technical leads from FAANG and tier-1 companies. If you want to really give it your best, mock interviews are a brilliant way to build confidence and get interview-ready.  

If you’re looking for the perfect resource to practice mock interviews with hiring managers from Apple and other FAANG companies, Interview Kickstart is everything you’re looking for.  

Join our FREE webinar to learn more.

Take Your Career to The Next Level

If you’re looking to take your professional career to the next level, enroll for Interview Kickstart’s Technical Interview Masterclass.

We’ve trained over 5,000 engineers to land dream offers from FAANG and tier-1 companies. Our instructors are hiring managers and technical leads at the biggest companies, helping our students gain a considerable edge while interviewing.

Sign up for our FREE webinar on How to Nail Your Next Tech Interview to learn more.

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