Facebook Interview Questions, Process, and Tips

Q1. What is the right age of employee to retire from any private company?
Ans. According to me my was 49 due to disability.
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Q2. Who is responsible for illegal rules?
Ans. 
The responsibility for illegal rules lies with the individuals or entities that create and enforce them.
• Illegal rules are typically created by individuals or organizations in positions of authority or power.

• Government bodies, legislative bodies, or regulatory agencies may be responsible for creating illegal rules.

• Enforcement agencies, such as the police or regulatory authorities, may be responsible for enforcing illega...read more
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Q3. Knowledge having is good or bad
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Q4. Nor good nor bad but must have complete instead having non or incomplete
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Q5. Why life is unbearable sometimes?
Ans. Might be thinking of view matter toward situation and time.
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Round duration - 90 minutes
Round difficulty - Hard

This was an online coding round where we were supposed to solve 2 questions under 90 minutes . Both the questions in my set were related to Graphs and were quite tricky and heavy to implement.

Q1. 
Path Counting in Directed Graph
Given a directed graph with a specified number of vertices V and edges E, your task is to calculate the total number of distinct paths from a given source node S to all ot...read more
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Steps: 

1) Create a recursive function that takes index of node of a graph and the destination index. Keep a global or a static variable count to store the count. Keep a record of the nodes visited in the current path by passing a visited array by value (instead of reference, which would not be limited to the current path).
2) If the current nodes is the destination increase the count.
3) Else for all the adjacent no...read more
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Q2. 
Course Schedule II Problem Statement
You are provided with a number of courses 'N', some of which have prerequisites. There is a matrix named 'PREREQUISITES' of size 'M' x 2. This matrix indicates that fo...read more
Ans. 
Approach : This problem was based on Topological Sorting .

The first node in the topological ordering will be the node that doesn't have any incoming edges. Essentially, any node that has an in-degree of 0 can start the topologically sorted order. If there are multiple such nodes, their relative order doesn't matter and they can appear in any order.

Algorithm : 

1) Initialize a queue, Q to keep a track of all the nod...read more
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Round duration - 60 Minutes
Round difficulty - Medium

This was a Data Structures and Algorithms round with some standard questions . I was expected to come up with an
efficient approach and code it as well .

Q1. 
Merge Intervals Problem Statement
You are provided with 'N' intervals, each containing two integers denoting the start time and end time of the interval.
Your task is to merge all overlapping intervals a...read more
Ans. 
Steps : 

1) First, we sort the list as described. 
2) Then, we insert the first interval into our merged list and continue considering each interval in turn as follows - 
2.1) If the current interval begins after the previous interval ends, then they do not overlap and we can 
append the current interval to merged. 
2.2) Otherwise, they do overlap, and we merge them by updating the end of the previo...read more
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Q2. 
Longest Route Problem Statement
Given a 2-dimensional binary matrix called Mat of size N x M that consists solely of 0s and 1s, find the length of the longest path from a specified source cell to a destina...read more
Ans. 
1. The idea is to reduce the problem from finding a path from source to destination to finding a path from some node to destination and building our answer up.
2. From the current cell, we look if there exists a neighbor from where I can reach the destination if no such neighbor exists we return -1.
3. Else if a path exists we take the longest path then add 1 in it ( to account for the transition from the current cell to a neighb...read more
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Round duration - 50 Minutes
Round difficulty - Medium

This was also a DSA round where I was asked to code only one of the questions but I eventually ended up coding both
as I had some spare time and explained my approches very smoothly to the interviewer . This round went preety well .

Q1. 
Longest Increasing Subsequence Problem Statement
Given an array of integers with 'N' elements, determine the length of the longest subsequence where each element is greater than the previous element. This...read more
Ans. 
Approach 1 (Using DP ) :

This is a classic Dynamic Programming problem.
Steps : 
1) Let dp[i] is the longest increase subsequence which ends at nums[i] . 
2) For every i from 0 to n , traverse backwards from j=i-1 to j=0 and check if nums[i]>nums[j].
3) If nums[i]>nums[j] , update dp[i]=max(dp[i] , dp[j]+1)
4) Finally return the maximum element from the DP array

TC: O(N^2)
SC: O(N)

Approach 2 (Using Binary Searc...read more
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Q2. 
Search In Rotated Sorted Array Problem Statement
Given a rotated sorted array ARR of size 'N' and an integer 'K', determine the index at which 'K' is present in the array.
Note:
1. If 'K' is not present...read more
Ans. 
This was a preety standard Binary Search Question and I had solved this question before on platforms like LeetCode and CodeStudio . I was asked this question to test my implementation skills and how well do I handle Edge Cases .

Approach :
1) The idea is to find the pivot point, divide the array in two sub-arrays and perform binary search.
2) The main idea for finding pivot is – for a sorted (in increasing order) and pivo...read more
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Round duration - 50 Minutes
Round difficulty - Medium

This was also a DSA round with 2 questions of Medium to Hard difficulty . I was expected to follow some clean code and OOPS principles to write the code in this round .

Q1. 
Rank from Stream Problem Statement
Given an array of integers ARR and an integer K, determine the rank of the element ARR[K].
Explanation:
The rank of any element in ARR is defined as the number of elem...read more
Ans. 
Step 1- Making the ‘BST’ :
 
Let insert(TreeNode* <int> ROOT, int VAL) be a function which insert data into ‘BST’.
Now consider the following steps to implement the function :
1. If ‘ROOT’ is NULL then make a new Node with data and return it.
2. If 'VAL' is less than data of ‘ROOT’ then do:
   1. Make a recursive call with the left child of ‘ROOT’ as ‘ROOT’.
   2. Increase the size of the left subtree of ‘ROOT’ by 1.
3. Otherwise do:
   1. Mak...read more
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Q2. 
LRU Cache Design Question
Design a data structure for a Least Recently Used (LRU) cache that supports the following operations:
1. get(key) - Return the value of the key if it exists in the cache; otherw...read more
Ans. 
Approach : 

Structure of an LRU Cache :

1) In practice, LRU cache is a kind of Queue — if an element is reaccessed, it goes to the end of the eviction order
2) This queue will have a specific capacity as the cache has a limited size. Whenever a new element is brought in, it
is added at the head of the queue. When eviction happens, it happens from the tail of the queue.
3) Hitting data in the cache must be done in const...read more
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Round duration - 60 Minutes
Round difficulty - Medium

This was a Data Structures and Algorithms round with preety good questions . I was expected to come up with an efficient approach and code it as well .

Q1. 
K Closest Points to Origin Problem Statement
Your house is located at the origin (0,0) of a 2-D plane. There are N neighbors living at different points on the plane. Your goal is to visit exactly K neighb...read more
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Q2. 
Power Set Generation
Given a sorted array of 'N' integers, your task is to generate the power set for this array. Each subset of this power set should be individually sorted.
A power set of a set 'ARR' i...read more
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Round duration - 50 Minutes
Round difficulty - Hard

This was also a DSA round where I was asked to code only one of the questions but I eventually ended up coding both as I had some spare time and explained my approches very smoothly to the interviewer . This round went preety well .

Q1. 
Roman Numeral to Integer Conversion
Convert a string representing a Roman numeral into its integer equivalent and return the result.
Explanation:
Roman numerals are represented by seven different symbol...read more
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Q2. 
Pair Sum Problem Statement
You are given an integer array 'ARR' of size 'N' and an integer 'S'. Your task is to find and return a list of all pairs of elements where each sum of a pair equals 'S'.
Note:
...read more
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Round duration - 50 Minutes
Round difficulty - Medium

This was also a DSA round with 2 questions . One was implementation heavy and the other was related to recursion and so I handled it carefully so that my code does not run into TLE or Segmentation Fault.

Q1. 
Arithmetic Expression Evaluation Problem Statement
You are provided with a string expression consisting of characters '+', '-', '*', '/', '(', ')' and digits '0' to '9', representing an arithmetic express...read more
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Q2. 
Remove Duplicates from Sorted Array Problem Statement
You are given a sorted integer array ARR of size N. Your task is to remove the duplicates in such a way that each element appears only once. The outpu...read more
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Round duration - 50 Minutes
Round difficulty - Medium

This was a typical System Design round where I was asked about the various features of Facebook and what sort of data structures and algorithms are used in implementing them .

Q1. How does Facebook store likes and dislikes?
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Q2. How does Facebook implement graph search?
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Round duration - 50 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.

Q1. What is Hadoop and why is it used?
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Q2. How does Facebook Chat work?
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Round duration - 75 minutes
Round difficulty - Easy

Timing it is around 11 am and Environment is good .

Q1. 
Bird and Maximum Fruit-Gathering Problem Statement
A ninja bird can gather fruits from trees arranged in a circle. Each tree has an associated fruit value. The bird can gather all the fruits from a tree i...read more
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Q2. 
Base 58 Conversion Problem Statement
You are given a decimal number 'N'. Your task is to convert this number into a base 58 representation.
The Base58 alphabet is defined by the following characters: “12...read more
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Round duration - 45 mintues
Round difficulty - Medium

Environment was very friendly but questions asked are hard

Q1. 
Pair Sum Problem Statement
You are provided with an array ARR consisting of N distinct integers in ascending order and an integer TARGET. Your objective is to count all the distinct pairs in ARR whose sum...read more
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Q2. 
Triplets with Given Sum Problem
Given an array or list ARR consisting of N integers, your task is to identify all distinct triplets within the array that sum up to a specified number K.
Explanation:
A t...read more
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