ADS Software Developer Interview Questions and Answers

Q1. Why you want to join facebook?
Ans. 
I want to join Facebook because of its innovative technology, global impact, and opportunities for growth.
• Innovative technology: Facebook is known for its cutting-edge technology and constant innovation.

• Global impact: Working at Facebook would allow me to contribute to a platform that connects billions of people worldwide.

• Opportunities for growth: Facebook offers a dynamic and fast-paced work environment with ample opp...read more
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Q2. Whats the best feature you like in Facebook?
Ans. 
I appreciate the personalized news feed feature on Facebook.
• Personalized news feed shows content based on user interests

• Helps users stay updated on relevant information

• Allows users to engage with content they are interested in
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Round duration - 90 minutes
Round difficulty - Hard

This was an online coding round where we had 2 questions to solve under 90 minutes . Both the questions were preety hard according to me . One has to have a fair share of knowledge in Data Structures and Algorithms to pass this round .

Q1. 
Longest Increasing Path in a 2D Matrix Problem Statement
Given a matrix of non-negative integers of size 'N x M', where 'N' and 'M' denote the number of rows and columns respectively, find the length of t...read more
Ans. 
The task is to find the length of the longest increasing path in a 2D matrix, where you can move in four directions: left, right, up, or down from each cell.
• Traverse the matrix and for each cell, find the longest increasing path starting from that cell

• Use dynamic programming to store the length of the longest increasing path for each cell

• Recursively explore all four directions from each cell, checking if the next cell ...read more
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Q2. 
Saving Money Problem Statement
Ninja is adventurous and loves traveling while being mindful of his expenses. Given a set of 'N' stations connected by 'M' trains, each train starting from station 'A' and r...read more
Ans. 
The task is to find the cheapest price from the given source to destination with up to K stops.
• Read the number of test cases

• For each test case, read the number of stations and trains

• Read the details of each train (source, destination, ticket price)

• Read the source station, destination station, and maximum number of stops

• Implement a graph data structure to represent the stations and trains

• Use a modified version of Dijkst...read more
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Round duration - 60 Minutes
Round difficulty - Medium

This Round was DS and Algo round and it started with formal introduction, followed by 2 problems. We first dicussed the
approach the time complexity and proper code covering all cases.

Q1. 
K - Sum Path In A Binary Tree
Given a binary tree where each node contains an integer value, and a value 'K', your task is to find all the paths in the binary tree such that the sum of the node values in ...read more
Ans. 
The task is to print every path of a binary tree with the sum of nodes in the path as 'K'.
• Traverse the binary tree and keep track of the current path and its sum

• At each node, check if the sum of the current path equals 'K'

• If yes, add the current path to the result

• Continue traversing the left and right subtrees recursively

• Remove the current node from the path before backtracking
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Q2. 
Combination Sum Problem Statement
Given an array of distinct positive integers ARR and a non-negative integer 'B', find all unique combinations in the array where the sum is equal to 'B'. Numbers can be c...read more
Ans. 
The task is to find all unique combinations in an array whose sum is equal to a given target sum.
• Use backtracking to generate all possible combinations

• Sort the array in non-decreasing order to ensure elements in each combination are in non-decreasing order

• Start with an empty combination and iterate through the array, adding each element to the combination and recursively calling the function with the remaining sum

• If th...read more
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Round duration - 50 Minutes
Round difficulty - Medium

This Round was DS/Algo + Core round and it started with formal introduction, followed by 3 problems. We first dicussed
the approach the time complexity and proper code covering all cases for the 2 coding problems . The last question was
related to OS and was a bit theoretical .

Q1. 
Merging Accounts Problem
Given a list ACCOUNTS where each element consists of a list of strings, with the first element being the name of the account holder, and the subsequent elements being the email ad...read more
Ans. 
The task is to merge accounts belonging to the same person based on common emails and return the merged accounts.
• Iterate through each account and create a mapping of emails to account holders

• Iterate through the mapping and merge accounts with common emails

• Sort the merged accounts and return the result
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Q2. 
Binary Tree Construction from Preorder and Inorder Traversal
The goal is to construct a binary tree from given preorder and inorder traversal lists of the tree nodes.
Example:
Input:
preorder = [1, 2, ...read more
Ans. 
The task is to construct a binary tree using the given inorder and preorder traversals.
• Use the preorder traversal to determine the root of the binary tree

• Use the inorder traversal to determine the left and right subtrees of the root

• Recursively construct the left and right subtrees

• Return the root node of the constructed binary tree
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Q3. Can you explain the concept of demand paging?
Ans. 
Demand paging is a memory management technique where pages are loaded into memory only when needed.
• Demand paging allows for efficient memory utilization by loading pages into memory on demand.

• It reduces the amount of initial memory required to start a process.

• When a page is needed but not in memory, a page fault occurs and the required page is loaded from disk.

• Demand paging allows for larger virtual memory space than p...read more
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Round duration - 60 minutes
Round difficulty - Medium

This was a preety intense round as I was grilled more on my System Design concepts but eventually I was able to
asnwers all the questions with some help from the interviewer.

General Tip : While preparing for Facebook Interviews , make sure you read and understand some of the most important features that Facebook incorporates like Graph Search , Adding a friend , Removing a friend , Storing Likes/Dislikes and so on. 
All these features are important to learn because at their core they are nothing but Data Structures used and implemented very elegantly . So before your next Facebook interview , do read these topics and be confident about your LLD as well as HLD skills.

Q1. How does Facebook store likes and dislikes?
Ans. 
Facebook stores likes/dislikes using a combination of databases and caching systems.
• Likes/dislikes are stored in a distributed database system like Cassandra or HBase.

• Each like/dislike is associated with a user and the content being liked/disliked.

• The database is sharded to handle the large volume of likes/dislikes.

• Caching systems like Memcached or Redis are used to improve read performance.

• Likes/dislikes can be stored...read more
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Q2. How does Facebook implement graph search?
Ans. 
Facebook implements graph search by indexing user connections and content to enable efficient search queries.
• Facebook indexes user connections and content to build a graph database.

• The graph database is used to store and retrieve information about users, their relationships, and their content.

• Graph search queries are executed by traversing the graph database to find relevant connections and content.

• Facebook uses variou...read more
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Q3. How does Facebook Chat work?
Ans. 
Facebook Chat is a real-time messaging system that allows users to send and receive instant messages.
• Facebook Chat uses a client-server architecture.

• It utilizes long polling or WebSockets for real-time communication.

• Messages are stored in a message queue for delivery.

• Chat messages are encrypted for security.

• Facebook Chat supports features like read receipts, typing indicators, and group chats.
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Round duration - 90 minutes
Round difficulty - Easy

This was MCQ+Coding round.

Q1. How can you check if two strings are anagrams of each other?
Ans. 
Check if two strings are anagrams by comparing the sorted versions of the strings.
• Sort both strings and compare if they are equal.

• Use a hashmap to store the frequency of characters in each string and compare the maps.

• Ignore spaces and punctuation when comparing the strings.
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Round duration - 90 minutes
Round difficulty - Easy

This was face to face interview round.

Round duration - 90 minutes
Round difficulty - Easy

This was face to face interview round.

Round duration - 90 Minutes
Round difficulty - Medium

Interview started at 11:00 am. It was an online round. During the coding round I submitted optimized solution and got full acceptance of the solutions.

Q1. 
Detect Cycle in a Directed Graph
You are provided with a directed graph composed of 'N' nodes. You have a matrix called 'EDGES' with dimensions M x 2, which specifies the 'M' edges in the graph. Each edge...read more
Ans. 
Detect cycle in a directed graph using depth-first search (DFS) algorithm.
• Use DFS to traverse the graph and detect back edges indicating a cycle.

• Maintain a visited array to keep track of visited nodes during traversal.

• If a node is visited again during traversal and it is not the parent node, then a cycle exists.

• Return true if a cycle is detected, false otherwise.
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Round duration - 80 Minutes
Round difficulty - Medium

Interview started at 10:00 am. Interview went well, I was able to connect with the interviewer and enjoyed the whole interview

Q1. 
Next Smallest Palindrome Problem Statement
Find the next smallest palindrome strictly greater than a given number 'N' represented as a string 'S'.
Explanation:
You are given a number in string format, a...read more
Ans. 
Find the next smallest palindrome greater than a given number represented as a string.
• Convert the string to an integer, find the next greater palindrome, and convert it back to a string.

• Handle cases where the number is a palindrome or has all digits as '9'.

• Consider both odd and even length numbers when finding the next palindrome.
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Round duration - 80 Minutes
Round difficulty - Medium

Interview started at 11:00 am. Interview went well.

Q1. 
Boundary Traversal of a Binary Tree
Given a binary tree of integers, your task is to return the boundary nodes of the tree in Anti-Clockwise direction starting from the root node.
Input:
The first line ...read more
Ans. 
Return the boundary nodes of a binary tree in Anti-Clockwise direction starting from the root node.
• Traverse the left boundary nodes in a top-down manner

• Traverse the leaf nodes from left to right

• Traverse the right boundary nodes in a bottom-up manner

• Handle cases where duplicates occur in the boundary nodes

• Implement the function without printing as printing is already managed
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