DE Shaw Interview Questions, Process, and Tips

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 - 150 Minutes
Round difficulty - Medium

This first round was the Online test which was 1 Hour 95 Minutes Long. It was Divided
as Follows.

1. Aptitude Section (Arithmetic + Analytical) 14 Questions – 26 Minutes
2. Technical MCQs( Computer Science) 14 Questions – 19 Minutes
3. Coding Question – 20 Minutes
4. Coding Question – 30 Minutes
5. Coding Questions :

Q1. 
Water Equalization Problem Statement
You are provided with an array ARR of positive integers. Each integer represents the number of liters of water in a bucket. The goal is to make the liters of water in ...read more
Ans. 
Given an array of water buckets, find the minimum liters of water to remove to make all buckets equal.
• Iterate through the array to find the most common water level

• Calculate the total liters needed to make all buckets equal by subtracting each bucket's water level from the most common level

• Sum up the total liters needed to remove
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Q2. 
K Max Sum Combinations Problem Statement
Given two arrays/lists A and B, each of size N, and an integer K, you need to determine the K maximum and valid sum combinations from all possible combinations of ...read more
Ans. 
The problem involves finding the K maximum sum combinations from two arrays by adding one element from each array.
• Iterate through all possible sum combinations of elements from arrays A and B.

• Store the sums in a max heap to keep track of the K maximum sums.

• Pop the top K elements from the max heap to get the K maximum sum combinations.
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Round duration - 150 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.

Q1. 
Minimum Fountains Activation Problem
In this problem, you have a one-dimensional garden of length 'N'. Each position from 0 to 'N' has a fountain that can provide water to the garden up to a certain range...read more
Ans. 
Find the minimum number of fountains to activate to water the entire garden.
• Iterate through the array to find the coverage of each fountain.

• Keep track of the farthest coverage reached by each activated fountain.

• Activate the fountain that covers the farthest distance not yet covered.

• Repeat until the entire garden is watered.
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Round duration - 150 Minutes
Round difficulty - Medium

This was also an Online F2F Technical Round conducted on Codepair : Hackerrank.
Dynamic Programming Based Not So Easy Level:
Best Time to Buy and Sell Stock
Best Time to Buy and Sell Stock II
Dynamic Programming Based Not So Medium Level
Best Time to Buy and Sell Stock with Cooldown
Best Time to Buy and Sell Stock with Transaction Fee
Dynamic Programming Based Hard Level
Best Time to Buy and Sell Stock III
Best Time to Buy and Sell Stock IV

They asked me a Lot of Questions like:
How did you arrive at this Solution ?
Why is this Approach Right ?
Can You do this in Better time & space complexities ? (Although I have done in Best time Complexity but they asked this to check my confidence level on my codes).
A lot of Variants based on Constraints.

Q1. 
Best Time To Buy and Sell Stock Problem Statement
You are given an array 'PRICES' of 'N' integers, where 'PRICES[i]' represents the price of a certain stock on the i-th day. An integer 'K' is also provide...read more
Ans. 
The task is to determine the maximum profit achievable with at most K transactions by buying and selling stocks.
• Iterate through the array and keep track of the minimum price to buy and maximum profit for each transaction.

• Use dynamic programming to store the maximum profit at each day with each possible number of transactions.

• Consider edge cases like when K is 0 or when the array is empty.

• Example: For input N = 6, PRICE...read more
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Q2. 
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 different combinations of buy a...read more
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Round duration - 95 Minutes
Round difficulty - Easy

This was a programming test consisting of 3 sections with 1 question each. 25 mins for the 1st section, and 35 for the 2nd and 3rd section. Each section had its own fixed time.

Q1. 
Majority Element - II Problem Statement
You are given an array ARR of integers of length N. Your task is to find all the elements that occur strictly more than floor(N/3) times in the given array.
Input:
...read more
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Q2. 
MegaPrime Numbers Problem Statement
Given two integers Left and Right, determine the count of 'megaprime' numbers within the inclusive range from 'Left' to 'Right'. A 'megaprime' number is a prime number ...read more
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Q3. 
Jump Game Problem Statement
In this problem, you are given an array ARR consisting of N integers. Your task is to determine the minimum number of jumps required to reach the last index of the array N - 1....read more
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Round duration - 70 Minutes
Round difficulty - Medium

There were two interviewers on a video call. For the first 25 minutes, the first interviewer asked his questions, and later the second one. For the second 25 minutes, questions related to OOPS were discussed, and also was asked to implement few things.

Q1. 
Alien Dictionary Problem Statement
You are provided with a sorted dictionary (by lexical order) in an alien language. Your task is to determine the character order of the alien language from this dictiona...read more
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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
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Round duration - 60-65 minutes
Round difficulty - Medium

It consisted of two coding problems which involved proper coding it and explaining each and every aspect and I have to show dry run over a few cases

Q1. 
Is Binary Heap Tree Problem Statement
You are given a binary tree of integers. Your task is to determine if it is a binary heap tree or not.
Input:
The first line of input contains an integer ‘T’ denoti...read more
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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
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Round duration - 20 minutes
Round difficulty - Easy

It was a very friendly and chill round.

Round duration - 80 minutes
Round difficulty - Easy

This round was scheduled in the evening hours around 7pm at Hackerrank platform and all the participants were required to fill a form which was shared 2 days prior to the test date. This form was filled out probably for the security reasons and to ensure that no one disinterested participant gives the test.

Q1. 
Ways To Make Coin Change
Given an infinite supply of coins of varying denominations, determine the total number of ways to make change for a specified value using these coins. If it's not possible to make...read more
Ans. 
The task is to find the total number of ways to make change for a specified value using given denominations.
• Use dynamic programming to solve this problem efficiently.

• Create a 2D array to store the number of ways to make change for each value up to the specified value.

• Iterate through each denomination and update the array accordingly.

• The final answer will be stored in the last cell of the array.

• Example: For N=3, D=[1, 2...read more
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Q2. 
Find the Duplicate Number Problem Statement
Given an integer array 'ARR' of size 'N' containing numbers from 0 to (N - 2). Each number appears at least once, and there is one number that appears twice. Yo...read more
Ans. 
Find the duplicate number in an array of integers from 0 to (N-2).
• Iterate through the array and keep track of the count of each number using a hashmap.

• Return the number with a count greater than 1 as the duplicate number.

• Alternatively, use Floyd's Tortoise and Hare algorithm to find the duplicate number in O(N) time and O(1) space.
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Round duration - 45 minutes
Round difficulty - Hard

This round was conducted on Zoom platform. I was shared the invitation link one day prior to the interview and also was told the name of my interviewer. I looked at the profile of the interviewer at linked.in and got a better understanding of what kind of person he was and prepared accordingly. The round was scheduled at 3 :00 pm on 20th August and I was eagerly waiting for the clock hands to reach 3 o'clock since morning and finally I went in front of him after wearing a white shirt and a black coat over it along with a tie over it.

Q1. 
First Negative Integer in Every Window of Size K
Given an array of integers 'ARR' and an integer 'K', determine the first negative integer in every contiguous subarray (or window) of size 'K'. If a window...read more
Ans. 
Find the first negative integer in every window of size K in an array.
• Iterate through the array using a sliding window approach of size K

• For each window, find the first negative integer and add it to the result array

• If no negative integer is found in a window, add 0 to the result array
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