Lenskart Software Developer Interview Questions and Answers

Round duration - 60 Minutes
Round difficulty - Medium

This round was purely based on Data Structures and Algorithms . One has to be fairly comfortable in solving Algorithmic problems to pass this round . Both the questions asked were quite common and luckily I had already prepared them from CodeStudio and LeetCode.

Q1. 
Binary Tree Traversals Problem Statement
Given a Binary Tree with 'N' nodes, where each node holds an integer value, your task is to compute the In-Order, Pre-Order, and Post-Order traversals of the binar...read more
Ans. 
Compute the In-Order, Pre-Order, and Post-Order traversals of a Binary Tree given in level-order format.
• Implement functions to perform In-Order, Pre-Order, and Post-Order traversals of a Binary Tree.

• Use level-order input to construct the Binary Tree.

• Traverse the Binary Tree recursively to generate the required traversals.

• Ensure proper handling of null nodes represented by -1 in the input.

• Return the three traversals as
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Q2. 
Reverse Linked List Problem Statement
Given a Singly Linked List of integers, your task is to reverse the Linked List by altering the links between the nodes.
Input:
The first line of input is an intege...read more
Ans. 
Reverse a singly linked list by altering the links between nodes.
• Iterate through the linked list and reverse the links between nodes

• Use three pointers to keep track of the current, previous, and next nodes

• Update the links between nodes to reverse the list

• Return the head of the reversed linked list
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Round duration - 45 Minutes
Round difficulty - Medium

This round basically tested some concepts from Data Structures and File Manipulation .

Q1. 
Intersection of Two Arrays Problem Statement
Given two arrays A and B with sizes N and M respectively, both sorted in non-decreasing order, determine their intersection.
The intersection of two arrays in...read more
Ans. 
The problem involves finding the intersection of two sorted arrays efficiently.
• Use two pointers to iterate through both arrays simultaneously.

• Compare elements at the pointers and move the pointers accordingly.

• Handle cases where elements are equal and update the intersection array.

• Return the intersection array as the result.
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Round duration - 60 minutes
Round difficulty - Easy

Two coding questions were given in the first round to be solved in 60 minutes.

Q1. 
Rearrange Array Elements Problem Statement
Given an array A containing 'N' integers and an integer m, rearrange the elements of the array such that the differences between the array elements and m are sor...read more
Ans. 
Rearrange array elements based on their differences from a given integer.
• Calculate the differences between each element and the given integer.

• Sort the elements based on their differences while maintaining the original order for elements with the same difference.

• Implement a function to rearrange the array elements as per the given criteria.
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Q2. 
Print Nodes at Distance K from a Given Node
Given an arbitrary binary tree, a node of the tree, and an integer 'K', find all nodes that are at a distance K from the specified node, and return a list of th...read more
Ans. 
The task is to find all nodes in a binary tree that are at a distance K from a given node.
• Traverse the binary tree to find the given node

• From the given node, perform a depth-first search to find all nodes at distance K

• Use a list to store the values of the nodes at distance K

• Return the list of values in any order
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Round duration - 60 minutes
Round difficulty - Easy

This was a technical round with questions based on DSA, DBMS, Computer Networking and project based questions.

Q1. 
Triangle of Numbers Pattern
Ninja is tasked with printing a triangle pattern based on a given number 'N' for any test case.
Example:
Input:
N = 4
Output:
   1
  232
 34545
4567654
Explanation:
The pat...read more
Ans. 
Print a triangle pattern of numbers based on a given number 'N'.
• Iterate through each row and print the numbers accordingly

• Use spaces to center-align the numbers in each row

• Increment the numbers in each row as per the pattern
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Q2. What is the difference between a web server and an application server?
Ans. 
Web server serves static content over HTTP, while application server runs dynamic content and business logic.
• Web server handles HTTP requests and responses, serving static content like HTML, images, and CSS.

• Application server executes business logic, runs dynamic content, and interacts with databases.

• Web server examples include Apache, Nginx, while application server examples include Tomcat, JBoss.

• Web server focuses on...read more
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Q3. How does the internet work?
Ans. 
The internet is a global network of interconnected computers that communicate using standardized protocols.
• The internet is made up of a vast number of interconnected networks of computers.

• Data is transmitted over the internet using protocols such as TCP/IP.

• Websites are hosted on servers connected to the internet, and users access them using web browsers.

• Internet Service Providers (ISPs) provide access to the internet f...read more
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Q4. Write a SQL query to find the nth highest salary.
Ans. 
SQL query to find the nth highest salary
• Use the 'SELECT DISTINCT' statement to get unique salary values

• Order the salaries in descending order using 'ORDER BY' clause

• Use 'LIMIT' and 'OFFSET' to get the nth highest salary
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Round duration - 30 minutes
Round difficulty - Easy

Typical HR round with behavioral problems.

Round duration - 60 Minutes
Round difficulty - Medium

This was a typical DS/Algo where I was asked to solve two questions related to Binary Trees and write the pseudo code for both of them followed by some theoretical questions related to Operating Systems.

Q1. 
K-th Largest Number in a BST
Given a binary search tree (BST) consisting of integers and containing 'N' nodes, your task is to find and return the K-th largest element in this BST.
If there is no K-th la...read more
Ans. 
Find the K-th largest element in a BST.
• Perform reverse in-order traversal of the BST to find the K-th largest element.

• Keep track of the count of visited nodes to determine the K-th largest element.

• Return -1 if there is no K-th largest element in the BST.
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Q2. 
Is Height Balanced Binary Tree Problem Statement
Determine if the given binary tree is height-balanced. A tree is considered height-balanced when:
1. The left subtree is balanced.
2. The right subtree is bala...read more
Ans. 
Determine if a given binary tree is height-balanced by checking if left and right subtrees are balanced and their height difference is at most 1.
• Check if the left subtree is balanced

• Check if the right subtree is balanced

• Calculate the height difference between the left and right subtrees

• Return 'True' if all conditions are met, otherwise return 'False'
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Q3. Can you explain the concepts of Zombie Process and Orphan Process in operating systems?
Ans. 
Zombie process is a terminated process that has completed execution but still has an entry in the process table. Orphan process is a process whose parent process has terminated.
• Zombie process is created when a child process completes execution but its parent process has not yet read its exit status.

• Zombie processes consume system resources and should be cleaned up by the parent process using wait() system call.

• Orphan p...read more
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Round duration - 60 Minutes
Round difficulty - Medium

This was also a Data Structures and Algorithm round where I was asked to solve 3 medium to hard level problems along with their pseudo code within 60 minutes .

Q1. 
Longest Substring Without Repeating Characters Problem Statement
Given a string S of length L, determine the length of the longest substring that contains no repeating characters.
Example:
Input:
"abac...read more
Ans. 
Find the length of the longest substring without repeating characters in a given string.
• Use a sliding window approach to keep track of the longest substring without repeating characters.

• Use a hashmap to store the index of each character in the string.

• Update the start index of the window when a repeating character is found.

• Calculate the maximum length of the window as you iterate through the string.

• Return the maximum le
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Q2. 
Problem: Search In Rotated Sorted Array
Given a sorted array that has been rotated clockwise by an unknown amount, you need to answer Q queries. Each query is represented by an integer Q[i], and you must ...read more
Ans. 
Search for integers in a rotated sorted array efficiently.
• Use binary search to efficiently search for integers in the rotated sorted array.

• Handle the rotation of the array while performing binary search.

• Return the index of the integer if found, else return -1.
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Q3. 
Count Subarrays with Sum Divisible by K
Given an array ARR and an integer K, your task is to count all subarrays whose sum is divisible by the given integer K.
Input:
The first line of input contains an...read more
Ans. 
Count subarrays with sum divisible by K in an array.
• Iterate through the array and keep track of the prefix sum modulo K.

• Use a hashmap to store the frequency of each prefix sum modulo K.

• For each prefix sum, increment the count by the frequency of (prefix sum - K) modulo K.

• Handle the case when prefix sum itself is divisible by K.

• Return the total count of subarrays with sum divisible by K.
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Round duration - 50 Minutes
Round difficulty - Medium

In this round , I was asked to code a simple question related to BST . After that I was asked the internal implementation of a Hash Map where I was supposed to design a Hash Map using any of the Hashing Algorithms that I know . This was preety challenging for me but I got to learn so much from it.

Q1. 
Ceil Value from BST Problem Statement
Given a Binary Search Tree (BST) and an integer, write a function to return the ceil value of a particular key in the BST.
The ceil of an integer is defined as the s...read more
Ans. 
Ceil value of a key in a Binary Search Tree (BST) is found by returning the smallest integer greater than or equal to the given number.
• Traverse the BST to find the closest value greater than or equal to the key.

• Compare the key with the current node value and update the ceil value accordingly.

• Recursively move to the left or right subtree based on the comparison.

• Return the ceil value once the traversal is complete.
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Q2. 
Design a Constant Time Data Structure
Create a data structure that maintains mappings between keys and values, supporting the following operations in constant time:
1. INSERT(key, value): Add or update t...read more
Ans. 
Design a constant time data structure to maintain mappings between keys and values with various operations.
• Use a hash table to achieve constant time complexity for INSERT, DELETE, SEARCH, and GET operations.

• Keep track of the number of key-value pairs for GET_SIZE operation.

• Check if the hash table is empty for IS_EMPTY operation.

• Return true or false for SEARCH operation based on key existence.

• Return the value associated...read more
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Round duration - 90 Minutes
Round difficulty - Hard

I found the online coding round of Flipkart to be quite difficult based on the constraints of the problem and their time limits. I coded the first problem quite easily but on the second and the third problem , my code could only pass a few test cases and gave TLE for most of them. Both the questions required very efficient solution and the last 5 to 10 Test Cases carried more weight than the rest so I didn't get through this round.

Q1. 
Print the Kth Digit
Given three non-negative integers N, M, and K, compute the Kth digit from the right in the number obtained from N raised to the power M (i.e., N ^ M).
Input:
The first line contains ...read more
Ans. 
The task is to find the Kth digit from the right in the number obtained from N raised to the power M.
• Iterate through the digits of N^M from right to left

• Keep track of the position of the current digit

• Return the digit at position K from the right
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Q2. 
The Skyline Problem
Compute the skyline of given rectangular buildings in a 2D city, eliminating hidden lines and forming the outer contour of the silhouette when viewed from a distance. Each building is ...read more
Ans. 
Compute the skyline of given rectangular buildings in a 2D city, eliminating hidden lines and forming the outer contour of the silhouette.
• Iterate through the buildings and create a list of critical points (x, y) where the height changes.

• Sort the critical points based on x-coordinate and process them to form the skyline.

• Merge consecutive horizontal segments of equal height into one to ensure no duplicates.

• Return the fin...read more
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Q3. 
Longest Palindromic Substring Problem Statement
You are provided with a string STR of length N. The goal is to identify the longest palindromic substring within this string. In cases where multiple palind...read more
Ans. 
Identify the longest palindromic substring in a given string.
• Iterate through the string and expand around each character to find palindromes

• Keep track of the longest palindrome found

• Return the longest palindrome with the smallest start index
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