LinkedIn Software Developer Interview Questions, Process, and Tips

Round duration - 60 minutes
Round difficulty - Medium

Technical round with questions based on DSA. Also, there was a discussion on my BTP project.

Q1. 
Longest Palindromic Subsequence Problem Statement
Given a string A consisting of lowercase English letters, determine the length of the longest palindromic subsequence within A.
Explanation:
• A subsequ...read more
Ans. 
The brute force solution is based on the idea that if the two ends of a string are the same, then they must be included in the longest palindrome subsequence. Otherwise, both ends cannot be included in the longest palindrome subsequence. So, recursion can be used here. 
Time Complexity of this approach would be exponential. 

This solution can be optimized using dynamic programming. 
Let dp[l][r] denote the ...read more
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Q2. 
Binary Tree to Doubly Linked List
Transform a given Binary Tree into a Doubly Linked List.
Ensure that the nodes in the Doubly Linked List follow the Inorder Traversal of the Binary Tree.
Input:
The fi...read more
Ans. 
The idea is to traverse all the leaves and connect them by changing their left and right pointers. We also need to remove them from the Binary Tree by changing left or right pointers in parent nodes. 
One way to solve this is to add the leaves at the beginning of the current linked list and update the head of the list using the pointer to head pointer. Since we insert at the beginning, we need to process leaves in ...read more
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Q3. 
Palindrome Permutation - Problem Statement
Determine if a permutation of a given string S can form a palindrome.
Example:
Input:
string S = "aab"
Output:
"True"
Explanation:
The permutation "aba" o...read more
Ans. 
The brute force solution is to run two loops, the outer loop picks all characters one by one, the inner loop counts the number of occurrences of the picked character. We keep track of odd counts. Time complexity of this solution is O(n2). 
We can do it in O(n) time using a count array. 
Steps : 
1. Create a count array of alphabet size which is typically 256. Initialize all values of count array as 0.
2. Tra...read more
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Round duration - 60 minutes
Round difficulty - Medium

Technical interview round where the interviewer asked me questions based on DSA , algorithms and my project. Large set of questions pertaining to DBMS.

Q1. 
Serialize and Deserialize Binary Tree Problem Statement
Given a binary tree of integers, your task is to implement serialization and deserialization methods. You can choose any algorithm for serialization...read more
Ans. 
Recursion can be used here. Once the parent node is processed, make recursive calls for the children node. 
For serializing the tree into a list : 
• If node is null, store -1 in list and return
• Store the data at current node in list.
• Call function recursively for left and right subtrees.
• Return the list.
For deserializing the list into a tree : 
• If there are no more elements in list, return null.
• Crea...read more
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Q2. 
Shuffle Two Strings
You are provided with three strings: A, B, and C. Your task is to determine if C is formed by interleaving A and B. A string C is considered an interleaving of A and B if:
• The lengt...read more
Ans. 
The idea is to start from the last element, swap it with a randomly selected element from the whole array (including last). Now consider the array from 0 to n-2 (size reduced by 1), and repeat the process till we hit the first element. 
Algorithm : 

To shuffle an array a of n elements (indices 0..n-1):
for i from n - 1 down to 1 do
j = random integer with 0 <= j <= i
exchange a[j] and a[i]

Time Complexity: O(...read more
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Round duration - 60 minutes
Round difficulty - Medium

This was a design round where I was grilled on my internship , projects and some new design questions were also asked.
Q1. Design a work flow model of the entire work done in your internship.
Q2. Design a workflow model of any one of the projects you did.

Q1. Describe a map-based design for implementing a code that checks for isomorphic words in a file.
Ans. 
Tip 1: Mapping of current characters can be stored in a map. 
To check for two strings to be isomorphic using a map :
1) If lengths of str1 and str2 are not same, return false.
2) Do following for every character in str1 and str2
a) If this character is seen first time in str1, then current of str2 must have not appeared before.
(i) If current character of str2 is seen, return false. Mark current character of str2 as v...read more
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Q2. 
Stack with getMin Operation
Create a stack data structure that supports not only the usual push and pop operations but also getMin(), which retrieves the minimum element, all in O(1) time complexity witho...read more
Ans. 
Use two stacks: one to store actual stack elements and the other as an auxiliary stack to store minimum values. 
The idea is to do push() and pop() operations in such a way that the top of the auxiliary stack is always the minimum. 

Push(int x) // inserts an element x to Special Stack 
1) push x to the first stack (the stack with actual elements) 
2) compare x with the top element of the second stack (t...read more
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Round duration - 60 minutes
Round difficulty - Medium

This was a online test round where I was given 3 DSA questions to be solved in 60 minutes.

Q1. 
Count Ways to Reach the N-th Stair Problem Statement
You are provided with a number of stairs, and initially, you are located at the 0th stair. You need to reach the Nth stair, and you can climb one or tw...read more
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Q2. 
Optimal Strategy for a Coin Game
You are playing a coin game with your friend Ninjax. There are N coins placed in a straight line.
Here are the rules of the game:
1. Each coin has a value associated wit...read more
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Q3. 
Generate All Parentheses Combinations
Given an integer N, your task is to create all possible valid parentheses configurations that are well-formed using N pairs. A sequence of parentheses is considered w...read more
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Round duration - 60 minutes
Round difficulty - Easy

Technical Interview round with questions based on DSA, UNIX commands , Web Security etc.

Q1. 
Find The Repeating And Missing Number Problem Statement
You are provided with an array nums which contains the first N positive integers. In this array, one integer appears twice, and one integer is missi...read more
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Q2. What is the difference between the 'ps' and 'top' commands?
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Q3. What is cross-site scripting (XSS)?
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Q4. How can you prevent SQL injection?
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Q5. What is the command to kill all running Java processes?
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Round duration - 60 minutes
Round difficulty - Medium

Questions based on designing. My first project as it was related to Image processing, so he also asked questions related to it.

Q1. Design a complete system for a traffic enforcement camera.
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Q2. How does JSON (JavaScript Object Notation) work?
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Q3. What software testing frameworks are you familiar with?
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Q4. What is the best protocol for storing images?
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Round duration - 30 minutes
Round difficulty - Easy

This was a typical HR round with questions related to my final year project and some behavioral problems.

Round duration - 60 minutes
Round difficulty - Easy

In first round they asked me 2 coding questions where he asked me to code as close as possible to the actual one.

Q1. 
Ninja and Sorted Array Merging Problem
Ninja is tasked with merging two given sorted integer arrays ARR1 and ARR2 of sizes 'M' and 'N', respectively, such that the merged result is a single sorted array w...read more
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Q2. 
Word Distance Calculation
Given a document represented as an array/list ARR of words with length N, find the smallest distance between two given words for multiple queries. The distance is defined as the ...read more
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Round duration - 60 minutes
Round difficulty - Easy

Then in the second round they asked a little about tree and told me to code 2 codes.

Q1. 
Level Order Traversal Problem Statement
Given a binary tree of integers, return the level order traversal of the binary tree.
Input:
The first line contains an integer 'T', representing the number of te...read more
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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
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Round duration - 30 minutes
Round difficulty - Easy

HR round with typical behavioral problems.

Round duration - 60 minutes
Round difficulty - Medium

This was a 1 hour online coding round on hackerrank platform. 3 DSA questions were given.

Q1. 
Stock Trading Maximum Profit Problem
Given the stock prices for 'N' days, your goal is to determine the maximum profit that can be achieved. You can buy and sell the stocks any number of times but can onl...read more
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Q2. 
Ninja's Complement Problem Statement
Every day, Ninja dreams of a number but does not understand its significance. Upon investigation, Ninja discovers that converting this number to binary, taking its com...read more
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Q3. 
Bit Majority Number Generation
You are given an array arr consisting of N integers. Construct a number from these integers such that, for each bit position, if the quantity of set bits (1s) is greater tha...read more
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Round duration - 60 minutes
Round difficulty - Easy

In this round, a DSA question was first asked. Then a lot of discussion regarding the various test cases around this question took place. (e.g, handing of -ve numbers , decimals , overflow etc).
Main concentration was just to get as many as test cases possible and an efficient solution as well.
And Some common question like why you coding in C++?

Q1. 
Sum of Digits Problem Statement
Given an integer 'N', continue summing its digits until the result is a single-digit number. Your task is to determine the final value of 'N' after applying this operation ...read more
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Q2. What are the advantages of Object-Oriented Programming (OOP)?
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Round duration - 60 minutes
Round difficulty - Easy

Again one coding question to be done on shared screen

Q1. 
Counting Triangles in Graphs
Given two graphs – a directed graph DIR_GRAPH and an undirected graph UNDIR_GRAPH – you are tasked with counting the number of triangles in each of the graphs.
Example:
In t...read more
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