Facebook Software Development Engineer Interview Questions and Answers

Round duration - 90 Minutes
Round difficulty - Medium

Q1. 
Longest Decreasing Subsequence Problem Statement
Given an array/list of integers ARR consisting of N integers, your task is to determine the length of the longest decreasing subsequence.
Explanation:
A ...read more
Ans. 
Find the length of the longest decreasing subsequence in an array of integers.
• Use dynamic programming to keep track of the length of the longest decreasing subsequence ending at each index.

• Initialize an array to store the length of the longest decreasing subsequence for each element.

• Iterate through the array and update the length of the longest decreasing subsequence for each element based on previous elements.

• Return t...read more
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Q2. 
Next Greater Element Problem Statement
Given a list of integers of size N, your task is to determine the Next Greater Element (NGE) for every element. The Next Greater Element for an element X is the firs...read more
Ans. 
Find the Next Greater Element for each element in a list of integers.
• Iterate through the list of integers from right to left.

• Use a stack to keep track of elements for which the Next Greater Element is not yet found.

• Pop elements from the stack until a greater element is found or the stack is empty.

• Assign the Next Greater Element as the top element of the stack or -1 if the stack is empty.
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Round duration - 90 minutes
Round difficulty - Easy

This round was held during university hours and consisted of 2 coding questions.

Round duration - 120 minutes
Round difficulty - Easy

Make sure you do no cutting and are clear about the approach you'd be following. 
 

Q1. What is the running median of an input stream?
Ans. 
Running median of an input stream is the median value of the numbers seen so far in a continuous stream of data.
• Maintain two heaps - a max heap for the lower half of the numbers and a min heap for the upper half.

• Keep the number of elements in the two heaps balanced or differ by at most 1.

• If the total number of elements is odd, the median is the root of the max heap. If even, it is the average of the roots of the two he...read more
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Round duration - 90 minutes
Round difficulty - Easy

Myntra had conducted a coding test on campus before the start of the placement season with 2 questions, one on stack and other on DP.
Tips : For the test, the DP question asked was pretty standard, on Longest Common Subsequence. The question on stacks, I don't remember what it was but it was also pretty straight forward. For the test, I would recommend to solve problem from GFG. If they do come to resume shortlisting, they are looking for people who have done good projects and internships.

Q1. 
Longest Common Subsequence Problem Statement
Given two strings STR1 and STR2, determine the length of their longest common subsequence.
A subsequence is a sequence that can be derived from another sequen...read more
Ans. 
The task is to find the length of the longest common subsequence between two given strings.
• Implement a function to find the longest common subsequence between two strings.

• Use dynamic programming to solve this problem efficiently.

• Iterate through the strings and build a matrix to store the lengths of common subsequences.

• Return the length of the longest common subsequence found.
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Round duration - 60 minutes
Round difficulty - Easy

The interview started off with questions on my general interest in Software Development. The first round had two coding questions, I was supposed to write the code on paper. 
For the questions, they asked me to code the solution first. And then gave a specific input and asked me to demonstrate step by step in my code, how it would lead to the correct answer.
Tips: It's ok if you can't code a general solution, if you can write a code which works for the particular input they have given then also it's ok with them. But be thorough with Data structures.

Q1. 
Add Two Numbers as Linked Lists
You are given two singly linked lists, where each list represents a positive number without any leading zeros.
Your task is to add these two numbers and return the sum as ...read more
Ans. 
Add two numbers represented as linked lists and return the sum as a linked list.
• Traverse both linked lists simultaneously while keeping track of carry from previous sum

• Create a new linked list to store the sum, updating the value and carry as needed

• Handle cases where one linked list is longer than the other by adding remaining digits with carry
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Round duration - 60 minutes
Round difficulty - Medium

I wasn't asked to write any code in this interview. They asked me some questions on Machine Learning, because of my projects in them. Then they asked me if I knew graph algorithms. Since I knew BFS and DFS, I told them. They asked the difference between the two. Then they asked me if I knew how to find the shortest distance between two points in a graph. I didn't know Dijkstra's properly but I knew it worked on the greedy approach so was able to tell that. Then they asked me how would I find the second shortest path. I tried to answer it with the same greedy approach, but couldn't arrive at the complete solution.
Tips: They ask a tough theoretical question. It's ok if you don't know the answer, they only look for your approach.

Q1. 
BFS Traversal in a Graph
Given an undirected and disconnected graph G(V, E) where V vertices are numbered from 0 to V-1, and E represents edges, your task is to output the BFS traversal starting from the ...read more
Ans. 
BFS traversal in a disconnected graph starting from vertex 0.
• Use a queue to keep track of nodes to visit next in BFS traversal

• Start traversal from vertex 0 and explore its neighbors first

• Continue exploring neighbors level by level until all nodes are visited

• Ensure to print connected nodes in numerical sort order
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Q2. 
DFS Traversal Problem Statement
Given an undirected and disconnected graph G(V, E), where V is the number of vertices and E is the number of edges, the connections between vertices are provided in the 'GR...read more
Ans. 
DFS traversal to find connected components in an undirected and disconnected graph.
• Perform DFS traversal on each vertex to find connected components

• Maintain a visited array to keep track of visited vertices

• Print the vertices of each connected component in ascending order
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Q3. 
Dijkstra's Shortest Path Problem
Given an undirected graph with ‘V’ vertices (labeled 0, 1, ... , V-1) and ‘E’ edges, where each edge has a weight representing the distance between two connected nodes (X,...read more
Ans. 
Dijkstra's algorithm is used to find the shortest path from a source node to all other nodes in a graph with weighted edges.
• Implement Dijkstra's algorithm to find the shortest path distances from the source node to all other nodes in the graph.

• Use a priority queue to efficiently select the next node with the shortest distance.

• Update the distances of neighboring nodes based on the current node's distance and edge weight...read more
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