DE Shaw Software Developer Interview Questions, Process, and Tips

Round duration - 120 Minutes
Round difficulty - Hard

Online Test Platform - HackerRank
Test Access Window – between 10:00 AM to 6:00 PM
Online Test Pattern –

Total Duration of Test – 120 mins
Total No. of Sections - 5
Section 1 – One Coding Question - Easy difficulty (20 mins)
Section 2 – One Coding Question - Medium difficulty (30 mins)
Section 3 – One Coding Question - Medium difficulty (30 mins)
Section 4 - Technical MCQs - 10 questions (20 mins)
Section 5 - Aptitude MCQs - 10 questions (20 mins)
Programming Sections (1, 2 and 3): This will have 3 coding questions with a time limit of 80 minutes. It is mandatory for you to attempt the 1st coding question before moving to the second question and third. You cannot revisit question/section once you proceed ahead
MCQ Sections (4 and 5): This will have 10 technical and 10 aptitude questions, with a time limit of 20 minutes each. Each correct answer will carry 2 marks and wrong answer will carry negative 0.5
Technical questions will cover Data structures & algorithms, Operating systems, Database systems, SQL and Networks.
Aptitude questions will cover Quantitative Aptitude, Problem solving and Logical & verbal Reasoning

Q1. 
Tower Building Problem Statement
Given an array 'ARR' of 'N' cubes, you need to construct towers such that each cube can either be placed on top of an existing tower or start a new one. The restriction is...read more
Ans. 
The task is to determine the minimum number of towers needed to stack cubes in a specific order.
• Iterate through the array of cubes and maintain a stack to keep track of towers.

• For each cube, check if it can be placed on an existing tower or start a new one.

• Update the stack based on the cube's size and count the number of towers needed.

• Return the minimum number of towers required.

• Example: For input N = 3, ARR = [3, 2, 1
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Q2. 
Minimum Removals Problem Statement
Given an array ARR of size N and an integer K, determine the minimum number of elements that must be removed from the array so that the difference between the maximum an...read more
Ans. 
The problem involves finding the minimum number of elements to remove from an array so that the difference between the maximum and minimum element is less than or equal to a given value.
• Iterate through the array and keep track of the minimum and maximum elements.

• Calculate the difference between the maximum and minimum elements.

• If the difference is greater than the given value, increment the count of elements to remove.

• ...read more
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Q3. 
Conquering the Best Kingdom Problem Statement
Aragorn, an influential ruler, aspires to expand his power by conquering more kingdoms. There are 'N' kingdoms numbered from 0 to N-1, forming a tree structur...read more
Ans. 
Given a tree structure of kingdoms, determine if it's possible to conquer more kingdoms than Aragorn by strategically choosing the starting kingdom.
• Start at the kingdom adjacent to Aragorn's initial kingdom

• Choose the kingdom that allows you to capture the most number of kingdoms in subsequent turns

• Consider the tree structure to plan your conquest strategically
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Round duration - 60 Minutes
Round difficulty - Medium

They called and asked me to choose a date and time I would be free in the upcoming week for my interview.
I chose 10th March 5 pm. 

Interviewer was pretty friendly. Started with some resume based questions. Asked me OS, DBMS and JAVA based questions. A coding question was asked to code. Asked me OOPS related questions too.

Q1. 
K Most Frequent Elements Problem Statement
Given an integer array ARR and an integer K, identify the K most frequent elements within ARR. Return these elements sorted in ascending order.
Example:
Input:
...read more
Ans. 
Identify K most frequent elements in an array and return them sorted in ascending order.
• Use a hashmap to store the frequency of each element in the array.

• Sort the elements based on their frequency in descending order.

• Return the first K elements from the sorted list.
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Round duration - 90 Minutes
Round difficulty - Medium

This round had 3 coding questions. The first two were of moderate level and the third one was a bit hard and was related to Dynamic Programming.

Q1. 
Maximum Number from Linked List Problem Statement
Given a linked list where each node contains a single digit, your task is to construct the largest possible number using these digits.
Objective:
Print ...read more
Ans. 
To find the maximum number that can be formed using the digits present in a linked list.
• Traverse the linked list and store the digits in an array

• Sort the array in descending order

• Concatenate the sorted array elements to form the maximum number
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Q2. 
Chocolate Distribution Problem
You are given an array/list CHOCOLATES of size 'N', where each element represents the number of chocolates in a packet. Your task is to distribute these chocolates among 'M'...read more
Ans. 
Distribute chocolates among students to minimize difference between largest and smallest packets.
• Sort the array of chocolates packets.

• Use sliding window technique to find the minimum difference between largest and smallest packets distributed to students.

• Return the minimum difference as the output.
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Q3. 
LCS of Three Strings Problem Statement
Given three strings A, B, and C, determine the length of the longest common subsequence present in all three strings.
Explanation:
A subsequence is derived by dele...read more
Ans. 
Find the length of the longest common subsequence among three strings.
• Use dynamic programming to solve this problem efficiently.

• Create a 3D array to store the lengths of common subsequences.

• Iterate through the strings to fill the array and find the longest common subsequence length.
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Round duration - 60 Minutes
Round difficulty - Medium

This round had 2 questions of DS/Algo to solve under 60 minutes and 2 questions related to Operating Systems.

Q1. 
Buy and Sell Stock Problem Statement
Imagine you are Harshad Mehta's friend, and you have been given the stock prices of a particular company for the next 'N' days. You can perform up to two buy-and-sell ...read more
Ans. 
The task is to determine the maximum profit that can be achieved by performing up to two buy-and-sell transactions on a given set of stock prices.
• Iterate through the array of stock prices and calculate the maximum profit that can be achieved by buying and selling at different points.

• Keep track of the maximum profit after the first transaction and the maximum profit overall by considering all possible combinations of bu...read more
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Q2. 
Count Smaller People on Right
You are provided with an array called HEIGHT that contains the heights of 'N' people standing in a queue. For each person in the array, compute the number of individuals on t...read more
Ans. 
Count the number of people to the right with a smaller height for each person in a queue.
• Iterate through the array from right to left and maintain a sorted list of heights encountered so far.

• Use binary search to find the position where the current height should be inserted in the sorted list.

• The count of smaller people to the right for each person can be calculated based on the index of insertion in the sorted list.
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Q3. Can you define processes and threads in operating systems?
Ans. 
Processes are instances of programs in execution, while threads are smaller units within a process that can execute independently.
• Processes are independent entities that contain program code, data, and resources.

• Threads are lightweight units within a process that share the same resources but can execute independently.

• Processes have their own memory space, while threads share the same memory space.

• Processes communicate ...read more
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Q4. What are the different types of semaphores?
Ans. 
Different types of semaphores include binary semaphores, counting semaphores, and mutex semaphores.
• Binary semaphores: Can only have two states - 0 or 1. Used for mutual exclusion.

• Counting semaphores: Can have multiple states. Used for resource allocation and synchronization.

• Mutex semaphores: Similar to binary semaphores but with additional features like priority inheritance and deletion safety.
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Round duration - 60 Minutes
Round difficulty - Medium

This round had 3 coding questions in which I first had to explain my approach with proper complexity analysis and then code up the solution. I found the first problem to be a bit on the harder side compared to the rest of the 2 problems.

Q1. 
Longest Increasing Path in a 2D Matrix Problem Statement
Given a matrix of non-negative integers of size 'N x M', where 'N' and 'M' denote the number of rows and columns respectively, find the length of t...read more
Ans. 
Find the length of the longest increasing path in a 2D matrix by moving in four directions.
• Use dynamic programming to keep track of the longest increasing path starting from each cell.

• Explore all four directions from each cell and recursively find the longest increasing path.

• Optimize the solution by storing the length of the longest increasing path starting from each cell.
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Q2. 
Gas Station Tour Problem
You are presented with a circular track consisting of several petrol pumps. Each petrol pump is indexed from 0 to N-1 and offers certain attributes:
• The quantity of petrol ava...read more
Ans. 
Find the first petrol pump from which a truck can start its journey and complete the circle.
• Iterate through each petrol pump and calculate the remaining petrol after reaching the next pump.

• If the remaining petrol is negative at any point, reset the starting point to the next pump.

• If the total remaining petrol at the end is non-negative, return the starting point as the answer.
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Q3. 
Rabbit Jumping Problem
Consider 'n' carrots numbered from 1 to 'n' and 'k' rabbits. Each rabbit jumps to carrots only at multiples of its respective jumping factor A_j (i.e., A_j, 2A_j, 3A_j, ...), for all ra...read more
Ans. 
Calculate uneaten carrots after rabbits jump on multiples of their jumping factors.
• Iterate through each carrot and check if it is divisible by any rabbit's jumping factor

• Keep track of uneaten carrots and return the count at the end

• Consider using a set to store eaten carrots for efficient lookup
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Round duration - 90 Minutes
Round difficulty - Hard

This round had 3 coding questions and the difficulty of the questions ranged from Moderate to Hard level.

Q1. 
Jump Game Problem Statement
You are given a list of points, and currently at point 0, your task is to determine if you can reach the last point N. At each point i, you can jump at most JUMP[i] length forw...read more
Ans. 
The task is to determine if it is possible to reach the last point in a list of points by jumping a certain distance at each point.
• Iterate through the list of points and check if it is possible to reach the last point by jumping the maximum distance at each point.

• Keep track of the farthest point that can be reached from the current point.

• If the farthest point that can be reached is greater than or equal to the last poi
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Q2. 
Problem Statement: Sibling Nodes
You are provided with a Binary Tree consisting of 'N' nodes, where each node holds an integer value. Your objective is to identify and list all nodes that do not possess a...read more
Ans. 
Identify and list nodes in a Binary Tree without siblings.
• Traverse the Binary Tree in level order and keep track of nodes without siblings.

• Check if each node has a sibling by comparing with its parent's other child.

• Output the values of nodes without siblings in ascending order.
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Q3. 
Minimum Steps for a Knight to Reach Target
Given a square chessboard of size 'N x N', determine the minimum number of moves a Knight requires to reach a specified target position from its initial position...read more
Ans. 
Calculate the minimum number of moves a Knight requires to reach a specified target position on a chessboard.
• Implement a function that calculates the minimum number of moves for a Knight to reach the target position on an NxN chessboard.

• Consider the possible movements of a Knight on a chessboard (2 squares in one direction and 1 square in a perpendicular direction).

• Use breadth-first search (BFS) algorithm to find the s...read more
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Round duration - 60 Minutes
Round difficulty - Medium

This round went for about 50-60 minutes where I had to code two questions related to DSA after discussing their approaches and time and space complexities and then I was asked some questions revolving around OOPS. The interviewer was quite freindly and helped me at some places where I was facing some difficulties.

Q1. 
Evaluate Reverse Polish Notation Problem Statement
You are provided with an arithmetic expression in Reverse Polish Notation represented as an array EXP. Your task is to calculate the value of this expres...read more
Ans. 
Evaluate arithmetic expression in Reverse Polish Notation using stack.
• Use a stack to keep track of operands and perform operations when encountering an operator.

• Iterate through the array of strings and push operands onto the stack, perform operation when an operator is encountered.

• Handle division using modular division to avoid floating point precision issues.

• Return the final result modulo 10^9 + 7 as specified in the
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Q2. 
LCA in a Binary Search Tree
You are given a binary search tree (BST) containing N nodes. Additionally, you have references to two nodes, P and Q, within this BST.
Your task is to determine the Lowest Com...read more
Ans. 
Find the Lowest Common Ancestor (LCA) of two nodes in a Binary Search Tree (BST).
• Traverse the BST from the root node to find the LCA of nodes P and Q.

• Compare the values of nodes P and Q with the current node's value to determine the LCA.

• If both nodes are on the same side of the current node, move to that side; otherwise, the current node is the LCA.

• Handle cases where one node is the ancestor of the other node.

• Example: ...read more
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Q3. What is the Diamond Problem in C++ and how can it be resolved?
Ans. 
Diamond Problem is a common issue in multiple inheritance in C++ where a class inherits from two classes that have a common base class.
• Diamond Problem occurs when a class inherits from two classes that have a common base class, leading to ambiguity in accessing members.

• It can be resolved in C++ using virtual inheritance, where the common base class is inherited virtually to avoid duplicate copies of base class members.

• ...read more
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Q4. What is meant by garbage collection in the context of Object-Oriented Programming (OOP)?
Ans. 
Garbage collection in OOP refers to automatic memory management by deallocating memory of objects no longer in use.
• Garbage collection is a process of automatically reclaiming memory occupied by objects that are no longer in use.

• It helps prevent memory leaks and ensures efficient memory usage.

• Languages like Java, C#, and Python have built-in garbage collection mechanisms.

• Garbage collection can be done using different al...read more
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Round duration - 60 Minutes
Round difficulty - Medium

This round consisted of two coding problems which involved proper coding it and explaining each and every aspect and showing the dry run over a few test cases was also necessary.

Q1. 
Phone Directory Search Directory
You are given a list/array of strings representing the contacts in a phone directory. The task is to perform a search based on a query string 'str' and return all contacts...read more
Ans. 
Implement a phone directory search feature to suggest contacts based on a given prefix query string.
• Iterate through the contact list to find contacts with the prefix matching the query string.

• Display suggestions as the user types each character of the query.

• Handle cases where no suggestions are found for a particular prefix by printing 'No suggestions found'.
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Q2. 
Bottom View of Binary Tree
Given a binary tree, determine and return its bottom view when viewed from left to right. Assume that each child of a node is positioned at a 45-degree angle from its parent.
N...read more
Ans. 
Return the bottom view of a binary tree when viewed from left to right.
• Traverse the tree in level order and keep track of horizontal distance and depth of each node

• For each horizontal distance, update the node in the map if it is deeper than the current node

• Return the values of the map in sorted order of horizontal distance
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Round duration - 95 minutes
Round difficulty - Easy

This round was conducted in Hackerrank portal for a total duration of 95 minutes and was divided into 4 sections.

1st Section : Aptitude Section : 14 questions , 28 minutes
2nd Section : Technical Section : 12 questions , 17 minutes
3rd Section :1 coding Questions : 20 minutes+30 minutes

This Round was Conducted on Hackerrank (Webcam Enabled).

Q1. 
Coin Game Problem Statement
Wong wants to borrow money from Dr. Strange, who insists Wong must win a coin game first. The game involves two players taking turns to remove one coin from either end of a row...read more
Ans. 
Given an array of coin values, determine the maximum value Wong can obtain by playing a coin game against Dr. Strange.
• Wong plays first and can remove one coin from either end of the array on each turn.

• The game ends when no coins are left, and the player with the highest total value wins.

• Consider different scenarios like having an odd or even number of coins in the array.
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Q2. 
Find Magic Index in Sorted Array
Given a sorted array A consisting of N integers, your task is to find the magic index in the given array, where the magic index is defined as an index i such that A[i] = i...read more
Ans. 
Find the magic index in a sorted array where A[i] = i.
• Use binary search to efficiently find the magic index in the sorted array.

• Check the middle element of the array and compare it with its index to determine the direction to search.

• Repeat the process on the left or right half of the array until the magic index is found or no more elements to search.
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Round duration - 120 minutes
Round difficulty - Medium

This was an Online F2F Technical Round conducted on CodePair : Hackerrank. So, Basically You have to Run and Submit ( Pass All Test cases) in the Interview Round also (Like normal Coding Test) in Codepair : Hackerrank & along with that You should have to explain your Code and Approach to the Interviewers.
The Interviewers were helpful and didn't hesitate in giving hints. 
Timing - 10:00 A.M to 12:00 P.M

Q1. 
Minimum Number of Taps to Water the Garden
Given a garden that extends along a one-dimensional x-axis from point 0 to point N, your task is to determine the minimum number of taps needed to water the enti...read more
Ans. 
Find the minimum number of taps needed to water the entire garden using given tap ranges.
• Iterate over taps and update the farthest point each tap can reach.

• Use a greedy approach to select the tap that can water the farthest point.

• If a tap can't water any point, return -1.

• Example: For ranges = [3, 4, 1, 1, 0, 0], tap at position 1 can water the entire garden.
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Q2. 
Money Saving in Bank Problem
Harshit wants to save up money for his first car by depositing money daily in the Ninja bank with a specific increment strategy.
Starting with 1 rupee on the first Monday, th...read more
Ans. 
Calculate the total money accumulated by Harshit in Ninja bank after N days with a specific increment strategy.
• Start with 1 rupee on the first Monday and increase by 1 rupee each day from Tuesday to Sunday.

• Each new Monday starts with an additional rupee more than the previous Monday's deposit.

• Calculate the total amount of money accumulated after N days for each test case.

• Example: For N = 2, total amount is 3 rupees; fo
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Round duration - 120 minutes
Round difficulty - Hard

A lot of Variants based on Constraints were asked in this Round. They will ask you to write the final code for every question before Submitting it(run all test cases) so you won’t get any hints after running test cases in the IDE. ( So don’t Submit your code before dry running it on a lot of Test Cases on pen & paper , they allow to use pen & blank paper at the time of Interviews) .The Interviewers tried to trick in case of time complexities even if you gave the best one. So try to be confident.

Q1. 
Buy and Sell Stock Problem Statement
Imagine you are Harshad Mehta's friend, and you have been given the stock prices of a particular company for the next 'N' days. You can perform up to two buy-and-sell ...read more
Ans. 
The task is to determine the maximum profit that can be achieved by performing up to two buy-and-sell transactions on a given set of stock prices.
• Iterate through the array of stock prices and calculate the maximum profit that can be achieved by buying and selling at different points.

• Keep track of the maximum profit after the first transaction and the maximum profit after the second transaction.

• Return the sum of these t...read more
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Q2. 
Stock Investment Problem Statement
You are given the prices of a particular stock over 'N' consecutive days. Your task is to find the maximum profit that can be obtained by completing at most two transact...read more
Ans. 
Find the maximum profit that can be obtained by completing at most two transactions of buying and selling a stock.
• Iterate through the array of stock prices and calculate the maximum profit that can be obtained by completing at most two transactions.

• Keep track of the maximum profit that can be obtained by selling the stock on each day after buying it on a previous day.

• Consider all possible combinations of two transactio...read more
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Round duration - 30 minutes
Round difficulty - Easy

This was a Telephonic Round (Audio Call). The HR was friendly and asked basic questions.
The timing was 2:00 PM to 2:30 PM.

Q1. 
Rabbit Jumping Problem
Consider 'n' carrots numbered from 1 to 'n' and 'k' rabbits. Each rabbit jumps to carrots only at multiples of its respective jumping factor A_j (i.e., A_j, 2A_j, 3A_j, ...), for all ra...read more
Ans. 
Calculate uneaten carrots by rabbits with specific jumping factors.
• Iterate through each carrot and check if any rabbit jumps on it.

• Use the jumping factors to determine which carrots will be eaten.

• Subtract the eaten carrots from the total to get the uneaten carrots.
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Round duration - 45 minutes
Round difficulty - Medium

Technical Interview round with questions on Core Subjects mainly.

Q1. What is the difference between C and C++?
Ans. 
C is a procedural programming language while C++ is an object-oriented programming language with features like classes and inheritance.
• C is a procedural programming language, while C++ is a multi-paradigm language with support for object-oriented programming.

• C does not support classes and objects, while C++ does.

• C uses structures for data organization, while C++ uses classes for data organization.

• C does not have featur...read more
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Q2. What is a virtual function?
Ans. 
A virtual function is a function in a base class that is declared using the keyword 'virtual' and can be overridden by a function with the same signature in a derived class.
• Virtual functions allow for dynamic polymorphism in object-oriented programming.

• They are used to achieve runtime binding and enable the implementation of the function to be determined during runtime.

• Example: virtual void display() = 0; in a base cla...read more
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Q3. What is inheritance in object-oriented programming?
Ans. 
Inheritance is a concept in object-oriented programming where a class inherits properties and behaviors from another class.
• Allows for code reusability by creating a new class based on an existing class

• Child class inherits attributes and methods of the parent class

• Can have multiple levels of inheritance (e.g. grandparent, parent, child classes)

• Example: class Dog extends Animal, where Dog inherits properties and methods
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Q4. What is the difference between a Default Constructor and a Copy Constructor in Object-Oriented Programming?
Ans. 
Default Constructor is a constructor that is automatically called when an object is created without any arguments. Copy Constructor is used to create a new object as a copy of an existing object.
• Default Constructor has no parameters, while Copy Constructor takes an object of the same class as a parameter.

• Default Constructor initializes the object with default values, while Copy Constructor creates a new object with the...read more
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Round duration - 40 minutes
Round difficulty - Easy

Technical Interview round with questions on Core Subjects mainly.

Q1. What are the types of access modifiers in C++?
Ans. 
The types of access modifiers in C++ are public, private, and protected.
• Public: accessible from outside the class

• Private: only accessible within the class

• Protected: accessible within the class and its subclasses
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Q2. What is the difference between DDL (Data Definition Language) and DML (Data Manipulation Language)?
Ans. 
DDL is used to define the structure of database objects, while DML is used to manipulate data within those objects.
• DDL is used to create, modify, and delete database objects like tables, indexes, etc.

• DML is used to insert, update, delete, and retrieve data from database tables.

• DDL statements include CREATE, ALTER, DROP, TRUNCATE, etc.

• DML statements include INSERT, UPDATE, DELETE, SELECT, etc.
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Q3. What are the key differences between a Primary Key and a Unique Key in a database management system?
Ans. 
Primary Key uniquely identifies each record in a table, while Unique Key ensures that all values in a column are distinct.
• Primary Key does not allow NULL values, while Unique Key allows one NULL value.

• A table can have only one Primary Key, but multiple Unique Keys.

• Primary Key is automatically indexed, while Unique Key may or may not be indexed.

• Primary Key is used to establish relationships between tables, while Unique ...read more
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Q4. What is the difference between DBMS and RDBMS?
Ans. 
DBMS is a software system that manages databases, while RDBMS is a type of DBMS that stores data in a structured format using tables.
• DBMS stands for Database Management System, which is a software system that allows users to interact with a database.

• RDBMS stands for Relational Database Management System, which is a type of DBMS that stores data in a structured format using tables with rows and columns.

• RDBMS uses Struct...read more
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Q5. What are the objectives of normalization in database management systems?
Ans. 
Normalization in database management systems aims to reduce data redundancy, improve data integrity, and optimize database performance.
• Eliminate data redundancy by breaking down data into smaller tables

• Reduce update anomalies by ensuring data is stored in a logical and consistent manner

• Improve data integrity by enforcing referential integrity constraints

• Optimize database performance by reducing the amount of redundant
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Round duration - 30 minutes
Round difficulty - Easy

HR round with typical behavioral problems.

Round duration - 60 minutes
Round difficulty - Medium

Started with the discussion why do you want to join DE shaw. Since prior to my current company, I was working with a finance based company so they asked why do you want to come back to finance base company. So they asked my about debentures, bonds, mortgages and other financial jargons.
Then they asked questions related to DSA, OS etc.

Q1. 
Find Triplets with Given Sum Problem Statement
Given an array ARR consisting of N integers, your task is to identify all distinct triplets within the array that sum up to a given integer K.
Explanation:
...read more
Ans. 
The task is to find all distinct triplets in an array that sum up to a given integer.
• Iterate through the array and use nested loops to find all possible triplets.

• Use a set to store unique triplets and avoid duplicates.

• Check if the sum of the triplet equals the target sum.

• Return the list of valid triplets or -1 if no such triplet exists.
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Q2. 
Minimum Number of Platforms Problem
Your task is to determine the minimum number of platforms required at a railway station so that no train has to wait.
Explanation:
Given two arrays:
• AT - represent...read more
Ans. 
Determine the minimum number of platforms needed at a railway station so that no train has to wait.
• Sort the arrival and departure times arrays in ascending order.

• Initialize two pointers for arrival and departure times, and a variable to keep track of the maximum number of platforms needed.

• Increment the platform count when a train arrives and decrement when a train departs.

• Update the maximum platform count as needed.

• Ret...read more
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Q3. What is the difference between internal fragmentation and external fragmentation in operating systems?
Ans. 
Internal fragmentation occurs when memory is allocated in fixed-size blocks, leading to wasted space within a block. External fragmentation occurs when free memory is fragmented into small chunks, making it difficult to allocate contiguous blocks.
• Internal fragmentation is caused by allocating fixed-size blocks of memory, leading to wasted space within a block.

• External fragmentation occurs when free memory is fragmented...read more
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Q4. Write an SQL query to find the employee with the nth highest salary.
Ans. 
SQL query to find the employee with the nth highest salary
• Use the ORDER BY clause to sort salaries in descending order

• Use the LIMIT clause to select the nth highest salary

• Join the employee table with the salary table to get the employee details
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Q5. How is Java platform independent?
Ans. 
Java is platform independent due to its bytecode and JVM.
• Java code is compiled into bytecode, which can run on any platform with a Java Virtual Machine (JVM)

• JVM acts as an intermediary between the Java code and the underlying platform, ensuring portability

• Developers write code once and it can be executed on any platform that has a compatible JVM

• Examples: Windows, macOS, Linux all can run Java programs without any chang
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Q6. What is the difference between an abstract class and an interface in Java?
Ans. 
Abstract class can have both abstract and non-abstract methods, while interface can only have abstract methods.
• Abstract class can have constructor, member variables, and methods with implementation.

• Interface can only have abstract methods and constants.

• A class can implement multiple interfaces but can only extend one abstract class.

• Example: Abstract class - Animal with abstract method 'eat' and non-abstract method 'sle
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