D E Shaw Interview Experience | Set 21 (For Internship)

All the answers discussed here are just the ones which i have given in the interview
(Don’t judge its correctness, these are just to tell you the type of questions which are asked in the interview).
Do try to solve these questions before directly going to the answers.

Technical Test-

1. Find lowest area pattern which can be repeated to form full rectangle (l, r less than or equal 100)

2. Find the Longest Continuous block after flipping k-bits in a binary string
I used brute force in both the questions(first complete, second partial).
I will suggest you to directly go for brute force, if you dont know the optimized solution(for hard problems). do not waste much time in building up the optimized one.

Technical Interview 1-

1. Types of request in Networking.(if you have written web development in your resume)
ans: GET and POST, they asked other methods too.

2. Difference b/w GET and POST request.
ans: query string in url in GET method. but they asked more differences that i didn’t know.

3. Maximum number of characters in a URL
ans: 256 (be careful, they will suggest you by asking some questions and you have to catch those suggestions)
i got that hint from this question and instantly replied that number of characters in url(GET method) can be 256 but in post no of characters in query string are unlimited.

4. Find Standard Deviation of a large array by dividing the array into multiple subarrays.
ans: firstly i discussed standard deviation formula, then about the actual meaning of standard deviation(variation from mean).
(i suggested some approach, but that was not correct.)

Again they asked to do the same for finding mean.
i did that and explained them, this was again a hint for previous question.
(i got that and gave an approach, they feel satisfied.)

Solving general mathematical formula using above method.
ans: i said that for any mathematical formula, you have to convert it into some property
which is additive in nature(by doing some operations), get that value for the full array
and after that again convert it to the desired one.

5. Circle puzzle
ans: https://www.geeksforgeeks.org/puzzle-round-table-coin-game/

6. Write heapify algorithm

void heapify(int heap[], int ind) {
   if (ind > size) return;
   int small = ind, l = 2 * ind, r = 2 * ind + 1;
   if (heap[ind] > heap[l] && l  heap[r] && r <= size) small = r;
   if (small != ind) heapify(heap, small);
}

7. Problems in the given recursive program and optimizing the code (recursive)

int sum(int x) {
    if (x == 1) return x;
        return x + sum(x - 1);
}

ans:
if x <= 0 then this may go into infinite loop
if x is very big then this function will use a lot of space in system stacks
i suggested to directly use formula (x * (x + 1)) / 2, but they asked for optimized recursive solution
then i suggested

int sum(int x) {
    if (x <= 1) return x;
    int a = sum(x / 2);
    if (x & 1) return 2 * a + (x / 2) * (x / 2) + x;
    else return 2 * a + x / 2 * x / 2;
}

8. Remove Loops in a Linked List
ans: I asked whether the linked list is single or has multiple pointers.
they said single
i asked about no of loops, they said multiple loops.
i replied multiple loops in a singly linked list not possible.

9. Set in c++(if c++ mentioned in the resume)
ans: All the elements are unique and in a sorted order.

10. Implement Set c++ and optimize the operations (INSERT, DELETE, UNION, INTERSECTION)
ans: took some time and then suggested BST, because all the elements are already in sorted order
(inorder traversal) in BST and insert, delete operation in log n time.
they asked time complexity for union and intersection,
i said n log n (which is not correct), later i corrected myself and replied O(n).
then they asked what if tree is skewed, then i changed data structure and suggested some new approaches, they were not satisfied then i said self-balancing trees(that was what they want).

11. What is AVL TREE (How it is Balanaced)
ans: discussed its properties and (L-R, R-L shifts)

12. How data is stroed in DATABASE(if dbms is mentioned)
ans: B+ tree
then discussion on B+ tree, its properties and its uses.

Technical Interview 2-

1. Discussion on my projects.

2. JAVA (Where it is used)(if java is mentioned)

3. OOPS Concept (Polymorphism, inheritance, Interface, Implements)

4. Puzzle: Given an array of times(integer). Transfer that array to another side of the river in minimum time.(given that atmost two elements can travel on the boat at one time).
ans: take an array [1, 2, 4, 7]. notice that if {1, 2} are travelling in the boat then they will require only 2(max(1,2)) units of time(not 1+2).
then i suggested that firstly {1, 2} will be sent to other size and 1 will return back(time taken 2(going) + 1(coming)).
then send {4, 7} and 2 will return back(time taken 7(going) + 2(coming)).
then again send {1, 2}(time taken 2(going)).
total time- 2+1+7+2+2 = 14 units.
generally, firstly send smallest two then take smallest(on right side) back. In next go, send largest two and take smallest element(on right side) back. repeat this until full array is transferred.

5. Threads (Write a Program which show creation of threads)(if you don't know much about threading, you can skip it).

6. Find Problems in #DEFINE SQUARE(x) x * x
ans: lets assume that there is a function(fun()) which returns integer value. then SQUARE(fun()) will be expanded to fun() * fun().
it has 2 major problems
* one is it increases time complexity.
* it can change some pointer, global data(basically shared memory).
another problem is in SQUARE(i++), it will be expanded to i++*i++ which is also problematic.
another is SQUARE(3+2), expand to 3+2*3+2 which results in 11(which is wrong).
the solution to above problem is Change definition to
#define SQUARE(x) (x) * (x)

7. Explain DFS in tree and graph.(explain it and also give examples).

8. Find Cycle in a Graph and also discuss back edges.

9. What are static, global, auto and extern variables and functions and where they are used?

10. Explain whole C compilation process
(do study these basic topics.)

11. SQL (Find Second Minimum of all the data in Marks Column, Which student has the lowest total, find total marks of a student with its id)
12. What are Indexes in database, explain all? How they are stored and why?(only if SQL is mentioned in resume).
13. Do all the above things in python (used dict).
14. yield and generators in python.

HR Interview-
1. How was your interview?
2. Is this your first experience? How was it?
3. Tell me about yourself.
4. Why DE Shaw?(try to convince that you are very much interested in their company).
5. Tell me your strengths and weakness.
6. Have you already prepared for these questions?
7. When have you found your weakness?
8. Have you prepared weakness only for interview purpose?

If you want then after each round you may ask some questions to the interviewee.
eg. you can ask about technologies, languages used in their company or about the environment.

Best of Luck for your Interviews.

All Practice Problems for D-E-Shaw !