John Lewis Interview Questions and Answers

Round duration - 60 Minutes
Round difficulty - Medium

There were 2 coding questions given in this round. One was related to Dynamic Programming and the second one was related to Recursion and Number Theory.

Q1. 
House Robber Problem Statement
Mr. X is a professional robber with a plan to rob houses arranged in a circular street. Each house has a certain amount of money hidden, separated by a security system that ...read more
Ans. 
House Robber problem where a robber wants to maximize stolen money without robbing adjacent houses in a circular street.
• Use dynamic programming to keep track of maximum stolen money at each house.

• Consider two cases: either rob the current house and skip the next, or skip the current house.

• Handle circular arrangement by considering the first and last houses separately.

• Example: For arr[] = {2, 3, 2}, the output is 3. Rob...read more
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Q2. 
Nth Fibonacci Number Problem Statement
Calculate the Nth term in the Fibonacci sequence, where the sequence is defined as follows: F(n) = F(n-1) + F(n-2), with initial conditions F(1) = F(2) = 1.
Input:
...read more
Ans. 
Calculate the Nth Fibonacci number efficiently using dynamic programming.
• Use dynamic programming to store and reuse previously calculated Fibonacci numbers.

• Start with base cases F(1) and F(2) as 1, then calculate subsequent Fibonacci numbers.

• Optimize the solution to avoid redundant calculations by storing intermediate results.

• Time complexity can be reduced to O(N) using dynamic programming.

• Example: For N = 5, the 5th F
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Round duration - 50 Minutes
Round difficulty - Medium

Standard Data Structures and Algorithms round where I was given 2 questions to solve , one was from Linked List and the other was related to Priority Queue / Quick Sort .

Q1. 
Intersection of Linked Lists Problem Statement
You are provided with two linked lists, L1 and L2, both sorted in ascending order. Generate a new linked list containing elements that exist in both linked l...read more
Ans. 
Given two sorted linked lists, find the intersection of elements in both lists and return a new sorted linked list.
• Traverse both linked lists simultaneously to find common elements

• Create a new linked list to store the intersecting elements

• Ensure the final linked list is sorted in ascending order

• Handle cases where there are no common elements between the lists
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Q2. 
Kth Largest Element Problem Statement
Ninja enjoys working with numbers, and Alice challenges him to find the Kth largest value from a given list of numbers.
Input:
The first line contains an integer 'T...read more
Ans. 
Find the Kth largest element in a given list of numbers.
• Sort the array in descending order.

• Return the Kth element from the sorted array.

• Handle multiple test cases efficiently.
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Round duration - 50 Minutes
Round difficulty - Easy

This round majorly focused on Real life appications of Data Structures and also revolved around Object Oriented Programming Style of writing code .

Q1. 
Data Structure with Insert, Delete, and GetRandom Operations
Design a data structure that supports four operations: insert an element, remove an element, search for an element, and get a random element. E...read more
Ans. 
Design a data structure with insert, delete, search, and getRandom operations, all in constant time.
• Use a combination of HashMap and ArrayList to achieve constant time operations.

• For insert operation, add the element to the ArrayList and store its index in the HashMap.

• For delete operation, swap the element to be deleted with the last element in the ArrayList, update the index in the HashMap, and then remove the last el...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. 
Design a Least Recently Used (LRU) cache data structure that supports get and put operations with capacity constraint.
• Implement a doubly linked list to maintain the order of keys based on their recent usage.

• Use a hashmap to store key-value pairs for quick access.

• When capacity is reached, evict the least recently used item before inserting a new item.

• Update the position of a key in the linked list whenever it is accesse
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Round duration - 45 Minutes
Round difficulty - Medium

This round was inclined towards some Low Level Design Principles and some concepts from Java .

Q1. Design a Railway Reservation System.
Ans. 
Design a Railway Reservation System
• Create a database to store train schedules, seat availability, and passenger information

• Implement a user interface for users to search for trains, book tickets, and view their reservations

• Include features like seat selection, payment processing, and ticket confirmation

• Handle scenarios like waitlisting, cancellations, and refunds

• Ensure data security and privacy of passenger information
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Q2. Why is Java considered platform-independent while the Java Virtual Machine (JVM) is platform-dependent?
Ans. 
Java is platform-independent because the code is compiled into bytecode that can run on any platform with a JVM, which is platform-dependent due to its reliance on the underlying hardware and operating system.
• Java code is compiled into bytecode, which can run on any platform with a JVM.

• JVM acts as an interpreter that translates bytecode into machine code specific to the underlying hardware and operating system.

• The JVM ...read more
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Round duration - 90 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. 
Minimum Cost to Buy Oranges Problem Statement
You are given a bag of capacity 'W' kg and a list 'cost' of costs for packets of oranges with different weights. Each element at the i-th position in the list...read more
Ans. 
Find the minimum cost to buy a specific weight of oranges using given cost list.
• Iterate through the cost list and find the minimum cost to achieve the desired weight

• Keep track of the minimum cost while considering available packet weights

• Return -1 if it is not possible to buy exactly W kg of oranges
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Q2. 
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. 
Find all paths in a binary tree where the sum of node values equals a given value 'K'.
• Traverse the binary tree using DFS and keep track of the current path and its sum.

• At each node, check if the current sum equals 'K' and add the path to the result if true.

• Continue traversal to the left and right child nodes recursively.

• Return the list of paths that sum up to 'K'.
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Round duration - 40 Minutes
Round difficulty - Medium

This round majorly focused on puzzles and some questions revolving around Computer Networks and the projects in my resume .

Q1. You have two wires of different lengths that take different times to burn. How can you measure a specific amount of time using these two wires?
Ans. 
Use two wires of different lengths to measure a specific amount of time by burning them simultaneously.
• Burn both wires at the same time, one wire will burn faster than the other.

• Measure the time it takes for the faster burning wire to completely burn.

• Calculate the specific amount of time by using the ratio of the lengths of the two wires.
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Q2. You have 3 ants located at the corners of a triangle. The challenge is to determine the movement pattern of the ants if they all start moving towards each other. What will be the outcome?
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Round duration - 30 Minutes
Round difficulty - Easy

This is a cultural fitment testing round .HR was very frank and asked standard questions. Then we discussed about my role.

Q1. What do you know about the company?
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Q2. Why should we hire you?
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