Decathlon Developer 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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Q1. Firstly our intro like personal information ,Education regarding questions..then the ask this your first job or experience..regarding any other job perferd then they will see your physical strength are you...read more
Ans. Same as per the ask questions..
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Round duration - 90 minutes
Round difficulty - Medium

This was a proctured online coding round where we had 2 questions to solve under 90 minutes . The questions were of easy to medium level I would say with some lenghty implementations .

Q1. 
Minimum Numbers Required Problem Statement
Given an array 'ARR' consisting of N integers, along with two integers, 'SUM' and 'MAXVAL', you need to determine the minimum number of integers to be added to t...read more
Ans. 
Determine the minimum number of integers to be added to an array to make its sum equal to a given value.
• Iterate through the array and calculate the current sum.

• Determine the difference between the target sum and the current sum.

• Add the minimum number of integers within the range of -MAXVAL to MAXVAL to reach the target sum.
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Q2. 
Maximum Sum Subsequence Problem Statement
Given an array of integers NUMS consisting of N integers and an integer K, determine the maximum sum of an increasing subsequence with exactly K elements.
Exampl...read more
Ans. 
Find the maximum sum of an increasing subsequence with exactly K elements in an array of integers.
• Iterate through the array and maintain a dynamic programming table to store the maximum sum of increasing subsequences ending at each index.

• For each element, check all previous elements to find the increasing subsequence with maximum sum ending at that element.

• Update the dynamic programming table with the maximum sum found...read more
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Round duration - 50 Minutes
Round difficulty - Medium

Standard Data Structures and Algorithms round . One has to be fairly comfortable in solving algorithmic problems to
pass this round with ease.

Q1. 
Check Whether Binary Tree Is Complete
You have been given a binary tree and your task is to determine if it is a Complete Binary Tree or not.
A Complete Binary Tree is defined as a binary tree where ever...read more
Ans. 
Check if a binary tree is a Complete Binary Tree or not based on given criteria.
• Traverse the binary tree level by level and check if all levels are completely filled except the last one.

• Ensure all nodes at the last level are positioned at the leftmost side.

• Use level order traversal to check for completeness of the binary tree.

• Example: For input 1 2 3 4 -1 5 6 -1 7 -1 -1 -1 -1 -1 -1, the output should be 1.
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Q2. 
Consecutive Elements
Given an array arr of N non-negative integers, determine whether the array consists of consecutive numbers. Return true if they do, and false otherwise.
Input:
The first line of inp...read more
Ans. 
Check if an array of integers consists of consecutive numbers.
• Iterate through the array and check if the absolute difference between consecutive elements is 1.

• Sort the array and check if the elements are consecutive.

• Use a set to store the elements and check if the size of the set is equal to the length of the array.
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Round duration - 40 Minutes
Round difficulty - Medium

This round majorly focused on my projects and some standard questions revolving around Operating Systems and DBMS.

Q1. How can you print numbers from 1 to 100 using more than two threads in an optimized approach?
Ans. 
Use multiple threads to print numbers from 1 to 100 in an optimized approach.
• Divide the range of numbers (1-100) among the threads to avoid duplication.

• Use synchronization mechanisms like mutex or semaphore to ensure proper order of printing.

• Consider using a shared data structure like a queue to coordinate the threads.

• Implement a mechanism to signal the threads when to start and stop printing.
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Q2. What are the advantages of using views in a database management system?
Ans. 
Views in a database management system provide data security, simplify complex queries, and improve performance.
• Enhanced security by restricting access to certain columns or rows

• Simplify complex queries by pre-defining joins and filters

• Reduce redundancy by storing commonly used queries as views

• Improve performance by storing pre-processed data in views

• Allow for data abstraction, making it easier to work with complex data
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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?
Add your answer
Q2. Why should we hire you?
Add your answer

They ask nothing only few questions on dsa

They ask previous projects knowledge

Q1. How indexing works internally?
Ans. 
Indexing in databases is a way to optimize search queries by creating a data structure that allows for faster retrieval of data.
• Indexing creates a data structure (like B-trees or hash tables) that maps keys to the locations of corresponding data entries.

• When a query is made, the database engine uses the index to quickly locate the relevant data entries instead of scanning the entire database.

• Indexes can be created on o...read more
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Q1. Intoduce yourself
Ans. 
I am a passionate software developer with experience in Java, Python, and web development.
• Experienced in Java and Python programming languages

• Proficient in web development technologies such as HTML, CSS, and JavaScript

• Strong problem-solving skills and ability to work in a team environment
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Q2. Your Projects
Ans. 
Developed a web application for tracking personal fitness goals
• Used React.js for front-end development

• Implemented RESTful APIs for data retrieval and storage

• Utilized MongoDB for database management
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