DEV Community: BrainQuest

Last coding interview at SimpleOS

BrainQuest — Fri, 15 Dec 2023 14:17:56 +0000

Context

The third interview has been completed successfully. Neal is astonished by your performance. He rarely sees a candidate completing it without any extra help. He mentions that he is going to announce it soon to HR. It is now time for you to go home and take some rest. You are wondering if you are finally done with all the technical interviews. You ask this question to Neal and he answers that there is no more technical interview on-site but for the role you have applied, which is a senior role, there is a last coding challenge which you will be doing at home. The SimpleOS HR Team will contact you by email soon. He congratulates you and mentions that he is looking forward to work with you once this last step is done. He is very confident this last step won't cause you any troubles. He tells you to go home and take some rest.

You arrive home exhausted. You lie down on the sofa and start thinking about the very long day you had. You feel accomplished and very happy about what you have achieved. After all the coding questions you have solved, you really believe that the role is a perfect match for your skills. While thinking about all that, you fall asleep...

You wake up the next day, it is 11:12am. You feel way better. A good breakfast and a black coffee is what you need. Once all consumed, you turn on your laptop and check your emails. As expected, there is a new email from the SimpleOS HR Team. You open it and start reading.

Email

Congratulations to have passed the first three coding interviews at SimpleOS. Orolo and Neal told me that you are the ideal candidate for our open role and believe that your contribution would be highly appreciated. Since the role you have applied to is a senior position, you need to complete a last step before we can discuss an offer. I believe that this has been already discussed with you yesterday with Neal. The last step is a coding challenge that you should complete at home alone. You are allowed to read any books and access the internet to search any information you might need. Once you are happy with your solution, please reply to this email with your code. We expect an answer within 48 hours. The next section will provide some background information and the description of your task. Good luck.

Background

In SimpleOS, a folder is represented with a structure with attributes name, files and subfolders. See below a JSON representation of a simple folder containing two files and without any subfolders.

(Ref 1)

{
  "name"    : "root",
  "files"   : ['readme.txt', 'hello.txt'],
  "subfolders" : []
}

To represent a folder with subfolders, we reuse the same structure defined above in the attribute subfolders. This can represent any number of subfolder levels. See below a JSON representation of a folder containing two levels of subfolders.

(Ref 2)

{
  "name"    : "root",
  "files"   : ['readme.txt', 'hello.txt'],
  "subfolders" : [
    {
      "name"    : "videos",
      "files"   : ['vid1.mpeg', 'vid2.mpeg', 'vid3.mpeg'],
      "subfolders" : []
    }, 
    {
      "name"    : "pictures",
      "files"   : ['pic1.jpg', 'pic2.jpg'],
      "subfolders" : [
        {
          "name"    : "holidays",
          "files"   : ['h1.jpg', 'h2.jpg'],
          "subfolders" : []
        }        
      ]
    }] 
}

Your Task

Given a folder f, a path and a filename, write a JavaScript function createFile(f, path, filename) which creates and returns a new folder structure where the new file filename is added to the folder path. The function createFile(f, path, filename) does not change any of its inputs. The position of the new added file is not relevant in the files array, it could be at the beginning or at the end. The parameter path is an array representing the relative path of the target folder. As an example, the evaluation of createFile(f, ['root', 'videos'], 'NEW.mpeg') should return the below folder structure.

When **f* points to the structure in (Ref 2)*

{
  "name"    : "root",
  "files"   : ['readme.txt', 'hello.txt'],
  "subfolders" : [
    {
      "name"    : "videos",
      "files"   : ['NEW.mpeg', 'vid1.mpeg', 'vid2.mpeg', 'vid3.mpeg'],
      "subfolders" : []
    }, 
    {
      "name"    : "pictures",
      "files"   : ['pic1.jpg', 'pic2.jpg'],
      "subfolders" : [
        {
          "name"    : "holidays",
          "files"   : ['h1.jpg', 'h2.jpg'],
          "subfolders" : []
        }        
      ]
    }] 
}

What do you do ?

Explore the web

Search your notes

Give up

Your solution is ready

Search your notes

After thinking again about the coding question, you feel that it is not such a small task but happy to know that you have 48 hours to craft your solution. You walk in circle in your apartment going from your bedroom to the living room thinking about your next step. The task mentioned on the email reminds you an assignment you did when studying algorithms when you were still a computer science student. You decide that finding your student notes is the right next step. You bring from your basement a couple of boxes where you stored all your student notes. After a few hours of digging, you found the notes from the algorithm course. They are still complete and readable. It is a large pile of papers which will take you a few hours to organize and read. After a short coffee break, you start working.

You finally found your notes about recursive data structures such as Cons, Tree and Tensor. You feel that you are touching the right topic which could help you greatly to solve the coding challenge. The notes contain the data structure definition but more importantly they are associated with some concrete coding implementations covering the methods add(...), remove(...) and contains(...).

After a couple of hours of writing code trying to reuse the discovered logic found in your notes, you produce the below code. When trying it, you initially felt overly excited because you saw the filename included in the target folder. But after a few seconds, you notice that the output is not totally correct.

function tail(xs) {
  return xs.slice(1)
}

function createFileBuggy(f, path, filename) {
  return {
    "name" : f.name,
    "files" : cons(filename, f.files),
    "subfolders" : f.subfolders.map(folder => createFileBuggy(folder, tail(path), filename))
  }
}

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Explore the web

To write your solution, you decide to use a simple code editor and node.js as a JavaScript interpreter. This allows you to keep a relatively simple setup. When starting to write your solution, you notice that console.log(...) cannot be used to display the output of the function createFile(...). It prints [Array] instead of the array content for nested structures. It is annoying since you wanted to use console.log(...) to validate your change. As an example, console.log(f) prints on your console :

When **f* points to the structure in (Ref 2)*

{
  name: 'root',
  files: [ 'readme.txt', 'hello.txt' ],
  subfolders: [
    { name: 'videos', files: [Array], subfolders: [] },
    { name: 'pictures', files: [Array], subfolders: [Array] }
  ]
}

While browsing the internet to find a simple solution to your problem, you find that other people have the same issue. In one coding forum, you discover that there exists a simple trick to overcome this limitation. Converting a JavaScript object to JSON could be the key. You continue your research until you find exactly what you search. A generic function producing, from a JavaScript object, a console printable text with all the information you require. Bingo! You wrap your findings the below function.

function prettyPrint(f) {
  console.log(
    JSON.stringify(f, null, "  ")
  )
}

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Give up

For two days, you tried everything you could. You explored the web, read coding books and checked codes you had written for previous projects, but none of that worked. You don't feel far but still cannot make it work fully. You decide to send an email before the 48 hours threshold to announce that you received and worked on the last coding challenge but didn't reach a solution. You connect to your email application and send an email to the SimpleOS HR Team. You include as an attachment the last version of your code to indicate where you got stuck.

After a few hours of waiting, you receive an email back. You start reading.

We are very sorry to hear that you were not able to achieve this last coding challenge. Firstly, we would like to thank you for trying this challenge, it was a pleasure to have you as a candidate. Secondly, we believe in self-improvement and would like to give you more time to achieve this task. Please take the time you need to build the right knowledge before attempting again to solve this coding challenge. You can contact us again when you feel ready. Finally, this coding challenge is not fundamentally different from the three previous ones you successfully completed. Therefore, we suggest you to have a second look at those. Good luck and we hope to hear from you very soon.

Go to the 1st coding interview

Go to the 2nd coding interview

Go to the 3rd coding interview

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Your solution is ready

After having spent the entire night working on your solution, you feel great. You finally got the various elements of your design correct and can test successfully your code with all the different cases. You put together a recursive algorithm which combines a mechanism to visit all the folders and adds the file only at the target folder. You refactored your code multiple times and reached a simple and comprehensive solution. You still have a few hours left to complete this challenge but decide that the sooner you sent it the better. You want to get this done before going to bed. The email is quickly written and you also include the source code of your solution as an attachment.

A few minutes later, you receive an email from the SimpleOS HR Team with the title :

Time to discuss your employment contract

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You are invited for a 3rd coding interview at SimpleOS

BrainQuest — Mon, 04 Dec 2023 08:19:47 +0000

Context

The second interview with Orolo went great and he is very happy about the solution you have designed and implemented. Right after the second coding challenge, he brings you back to the cafeteria where you meet Neal, a technical leader from the recruiting team. Orolo congratulates you again for the first two interviews and leaves you with Neal. You can guess that Neal is older than Orolo and looks to have a more senior position in the company. Neal tells you about the daily tasks of his team and gives you more details about the vision of the team. His goal is to clarify what you will be doing if you get hired. His team's responsibility is to implement features related to the SimpleOS folder system. As an example, they have implemented features allowing users to navigate, sort and search files in SimpleOS. You appreciate his explanations and thank him. Neal mentions that he would like to evaluate your coding skills relevant in his area of work and brings you to a new room, close to his office. The room is larger than the one you were previously in. When you enter the room, you see a shelf, a table, a sofa, a water machine and a computer on the table. You see another envelope lying on the table. Neal tells you that you can take the time you need to solve the coding challenge described in the envelope. Before leaving, he says that his desk is located just in front of this office and you can come whenever you are ready. After a moment of hesitation, you sit on the sofa and open the envelope. It contains two letters, Background and Your Task. You start reading.

Background

(Ref 1)

{
  "name"    : "root",
  "files"   : ['readme.txt', 'hello.txt'],
  "subfolders" : []
}

(Ref 2)

{
  "name"    : "root",
  "files"   : ['readme.txt', 'hello.txt'],
  "subfolders" : [
    {
      "name"    : "videos",
      "files"   : ['vid1.mpeg', 'vid2.mpeg', 'vid3.mpeg'],
      "subfolders" : []
    }, 
    {
      "name"    : "pictures",
      "files"   : ['pic1.jpg', 'pic2.jpg'],
      "subfolders" : [
        {
          "name"    : "holidays",
          "files"   : ['h1.jpg', 'h2.jpg'],
          "subfolders" : []
        }        
      ]
    }] 
}

Your Task

Given a folder f and a string s, write a JavaScript function search(f, s) searching all the files in f (subfolders included) containing in their name, s. The function search(f, s) should not change any of its inputs and returns an array of all files found (key-sensitive match). The function search(f, s) should be able to search any folders regardless of the number of subfolder levels. As an example, evaluating search(f, 'h') when f points to the structure (Ref 2), should return :

[
  'root/hello.txt',
  'root/pictures/holidays/h1.jpg',
  'root/pictures/holidays/h2.jpg'
]

What do you do ?

Investigate the shelf

Explore the computer

Give up

Your solution is ready

Investigate the shelf

In the room, there is a massive shelf against the wall located on the left side of the table. On the shelf, you notice a large screen and a camera, probably used for video meetings. Its lower portion is filled with books. Without making any noise, you approach the shelf and start looking at the books it contains. You see books from the following subjects : marketing, communication and accounting, nothing exciting. You start to believe that you won't find anything useful to solve the coding challenge, but you suddenly notice a closed drawer located at the bottom of the shelf. You hesitate a second but finally open the drawer to investigate what it contains. You find some coding books. One book particularly attracts your attention because it has a marked page. The book title is "JavaScript: The Good Parts" by Douglas Crockford. You open the book at the marked page and start reading. After some time, you put back the book at its exact place, close the drawer and return to your desk.

To look at the page, click here

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Explore the computer

The computer, compared to the previous one you have used at SimpleOS, looks brand new. It has a large touch screen and is really quiet. All the software needed for coding are already installed. When you turned on the computer you had access, without entering any password, to a terminal, a coding editor and a Javascript interpreter. All those software are opened in a full screen mode which you seem not be able to minimize. You have the idea, like during the previous interview, to check the access given to the code editor. When doing so you discover that this time, unfortunately, the software permission is linked to a guest account which stops you to explore the entire file system. After a moment of reflection, you decide to try one last thing. You have in mind the shortcut-key to minimize all the windows on your personal computer. When applying the same shortcut, suddenly all the windows got minimized. You look around to make sure to be alone then slowly start looking. You see a background image and the trash icon. Without hesitation, you quickly open the trash and found a file named tmp. After reading the file and thinking about it for a few minutes, you decide that it is wiser to close it.

function head(xs) {
  return xs[0]
}

function tail(xs) {
  return xs.slice(1)
}

function size(xs) {
  return xs.length
}

function flat(xs) {
  if (size(xs) < 1) return xs
  return head(xs).concat(flat(tail(xs)))
}

console.log(flat([[1, 2], [3, 4], [], [5]]))

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Give up

After spending hours searching the right logic to solve the coding challenge, you start believing that you are not prepared enough and you require more time to improve your programming skills. You feel hopeless and think that it is time to announce your decision to Neal. You walk out of the room and easily find Neal in his office. He looks to be very busy with his job but stops working and brings all his attention to you. You announce your decision to give up. He tells you that he feels sorry but nevertheless asks your reasons. You mention all the ideas you had to solve the coding problem but none worked. He mentions that overall, you did well in the interview process and suggests you to read the book "The Little Schemer" by Friedman and Felleisen. Although this book is not about Javascript, it is an introduction to recursive thinking and Neal believes that it can improve your programming skills. He asks you to call him when you feel ready to attempt the coding challenge again.

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Your solution is ready

After a few attempts that took you a couple of hours, you feel great because you finally got a working solution. After cleaning your code, you finally decide to find Neal. You get out of the room and easily find Neal in his office. He lays on his sofa and tells you that he was waiting for your visit. You announce proudly that you have finally completed the coding challenge and are willing to share with him your solution. He looks very happy to hear that and starts asking you a few questions related to the logic of your code. From his computer, he connects to your session and starts reading and trying your code to validate your solution. Your solution is flawless. He then shows you his code which allows you to compare his solution with yours.

function head(xs) {
  return xs[0]
}

function tail(xs) {
  return xs.slice(1)
}

function size(xs) {
  return xs.length
}

function cons(x, arr) {
  return [x].concat(arr)
}

function flat(xs) {
  if (size(xs) < 1) return xs
  return head(xs).concat(flat(tail(xs)))
}

function search(f, s) {
  return searchCalc(f, s, "")
}

function searchCalc(f, s, path) {
  return f.files
    .filter(file => file.includes(s))
    .map(file => path + f.name + "/" + file)
    .concat(
      flat(f.subfolders.map(folder => searchCalc(folder, s, path + f.name + "/")))
    )
}

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You are invited for a 2nd coding interview at SimpleOS

BrainQuest — Mon, 27 Nov 2023 08:06:00 +0000

Context

SimpleOS has been impressed with the solution you have provided in the first interview. They invited you for a second interview. The second interview, like the first one, is located in their headquarter building. When you arrive at the company, you meet Orolo who seems happy to see you again. He congratulates you for passing the first interview and brings you to the cafeteria so that you can both chat around a coffee. He gives you more information about the role you have applied and explains that the company is searching for candidates with strong analytical and core programming skills. He would like to continue evaluating your JavaScript coding skills in this second interview with the same process used previously. You mention that this works for you and are ready to start. You both start walking in company building for a few minutes following various corridors and taking a lift to the 24th floor. He brings you to a room where you see a table, a shelf, a chair and a coffee machine. On the table, you see a computer, a phone, a bottle of water, pen, papers and an envelope. Orolo tells you that the envelope contains the coding challenge and you can use anything at your disposal in this room while working on the challenge. Before leaving the room, he tells you that he is going to come back in 120 minutes and if you have any questions, you can simply call him with the phone by dialing #42494.

What do you do ?

Open the envelope

Call Orolo

Search the computer

Your solution is ready

Open the envelope

You open the envelope and notice that it contains two letters, Background and Your Task. You start reading.

Background

(Ref 1)

{
  "name"    : "root",
  "files"   : ['readme.txt', 'hello.txt'],
  "subfolders" : []
}

(Ref 2)

{
  "name"    : "root",
  "files"   : ['readme.txt', 'hello.txt'],
  "subfolders" : [
    {
      "name"    : "videos",
      "files"   : ['vid1.mpeg', 'vid2.mpeg', 'vid3.mpeg'],
      "subfolders" : []
    }, 
    {
      "name"    : "pictures",
      "files"   : ['pic1.jpg', 'pic2.jpg'],
      "subfolders" : [
        {
          "name"    : "holidays",
          "files"   : ['h1.jpg', 'h2.jpg'],
          "subfolders" : []
        }        
      ]
    }] 
}

Your Task

Given a folder f as an input, write a JavaScript function sort_asc(f) sorting the folder f ascendingly (also called the lexicographic order). The function sort_asc(f) does not change f but builds and returns a new folder structure with its elements sorted. The function sort_asc(f) should be able to sort any folder representation regardless of the number of subfolder levels. You are also provided with the code of the function show(f) which can be found here. As an example, when evaluating show(sort_asc(f)) where f points to the structure (Ref 2), the result should be :

root
..hello.txt
..readme.txt
..pictures
....pic1.jpg
....pic2.jpg
....holidays
......h1.jpg
......h2.jpg
..videos
....vid1.mpeg
....vid2.mpeg
....vid3.mpeg

Back to your actions

Call Orolo

After reading the question in the envelope, you have some doubt about which sorting functions you should use, can you reuse a sorting function already available in the JavaScript standard library or do you have to code a new one ? You pick up the phone and dial #42494. Orolo answers your call immediately and listen to your question. Here is what he answered before hanging up.

Orolo :

"Thanks for calling me and asking me this question. It is true that the JavaScript array prototype contains already a funtion sort() but unfortunately it creates a side effect by modifying the array which will change the input parameter f. In this coding challenge, the input should not be changed by the function sort_asc(f), therefore I suggest you to write your own sorting function. The performance of the sorting function is not important, you can decide to go with any methods. Good luck with this challenge."

Back to your actions

Search the computer

On the computer you are using to solve the code challenge, all the tools required for you to work are already installed and running, mainly a JavaScript interpreter (node.js), an editor and a console. You try to open the OS folder explorer, to search for any useful information, but you get an error message stating that you have not the required access level to proceed. After a moment of reflexion, you decide to check the access given to the editor and discover that the editor was launched with Administrator rights. You get very excited by this discovery which means that you can explore and open any files on that computer within this editor. While you explore the computer files, you find a file called quick_sort_asc.js. You decide to open the file and start reading.

function head(xs) {
  return xs[0]
}

function tail(xs) {
  return xs.slice(1)
}

function size(xs) {
  return xs.length
}

function cons(x, arr) {
  return [x].concat(arr)
}

function sortFiles(arr) {
  if (size(arr) < 1) return []
  let p = head(arr)
  let left = tail(arr).filter(x => x <= p)
  let right = tail(arr).filter(x => x > p)
  return sortFiles(left).concat(cons(p, sortFiles(right)))
}

function sortSubfolders(arr) {
  if (size(arr) < 1) return []
  let p = head(arr)
  let left = tail(arr).filter(x => x.name <= p.name)
  let right = tail(arr).filter(x => x.name > p.name)
  return sortFiles(left).concat(cons(p, sortFiles(right)))
}

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Your solution is ready

You are finally ready with your solution. You call Orolo and tells him that your code is ready. After a few minutes of waiting, he enters the room. He smiles and asks how it went. You mention that it was really not easy, but you were finally able to produce a simple piece of code able to solve the coding challenge. He asks you to explain your code logic and start listening to you. He seems happy with your explanations and shows you his solution. You both start comparing the two pieces of code.

function head(xs) {
  return xs[0]
}

function tail(xs) {
  return xs.slice(1)
}

function size(xs) {
  return xs.length
}

function cons(x, arr) {
  return [x].concat(arr)
}

function sortFiles(arr) {
  if (size(arr) < 1) return []
  let p = head(arr)
  let left = tail(arr).filter(x => x <= p)
  let right = tail(arr).filter(x => x > p)
  return sortFiles(left).concat(cons(p, sortFiles(right)))
}

function sortFolders(arr) {
  if (size(arr) < 1) return []
  let p = head(arr)
  let left = tail(arr).filter(x => x.name <= p.name)
  let right = tail(arr).filter(x => x.name > p.name)
  return sortFiles(left).concat(cons(p, sortFiles(right)))
}

function sort_asc(f) {
  return {
    "name" : f.name,
    "files" : sortFiles(f.files),
    "subfolders" : sortFolders(f.subfolders).map(sf => sort_asc(sf))
  }
}

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You are invited for a 1st coding interview at SimpleOS

BrainQuest — Mon, 20 Nov 2023 18:22:50 +0000

Context

You are invited for a first interview at the company SimpleOS. You meet the first interviewer, Orolo, which gives you more details about the programming role you have applied to. He offers you water and coffee, and tells you that this interview aims to evaluate your coding skills. He brings you to a room where you have access to a computer (without internet connection), a coffee machine, a pen and some blank papers. On the table, you can see a paper containing the coding question. Orolo tells you that the computer is already configured with the necessary tools (editor, interpreter, compiler) and you can use all the items at your disposal to solve the coding question. He leaves you alone saying that he will come back in 90 minutes to evaluate your progress.

Your actions

Read the question

Ask a hint

Think simple

Your solution is ready

Question

Background

(Ref 1)

{
  "name"    : "root",
  "files"   : ['readme.txt', 'hello.txt'],
  "subfolders" : []
}

(Ref 2)

{
  "name"    : "root",
  "files"   : ['readme.txt', 'hello.txt'],
  "subfolders" : [
    {
      "name"    : "videos",
      "files"   : ['vid1.mpeg', 'vid2.mpeg', 'vid3.mpeg'],
      "subfolders" : []
    }, 
    {
      "name"    : "pictures",
      "files"   : ['pic1.jpg', 'pic2.jpg'],
      "subfolders" : [
        {
          "name"    : "holidays",
          "files"   : ['h1.jpg', 'h2.jpg'],
          "subfolders" : []
        }        
      ]
    }] 
}

Your Task

Given a folder f as an input, write a JavaScript function show(f) printing on the console the folder f. See in section Output below the expected print format. The function show(f) should be able to print any folder representation regardless of the number of subfolder levels. You can assume that f is always a valid folder structure.

Output

When evaluating show(f) with (Ref 2) as its input, we obtain :

root
..readme.txt
..hello.txt
..videos
....vid1.mpeg
....vid2.mpeg
....vid3.mpeg
..pictures
....pic1.jpg
....pic2.jpg
....holidays
......h1.jpg
......h2.jpg

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Hint

After 20 minutes, Orolo comes back to the room to verify that you can work comfortably with the computer and asks you if you need anything. You mentioned that the computer setup is great and the question is very clear. You also indicate that you made some progress but, if possible, will be nice to get a small help to finalize your solution. Orolo states that it is possible and suggests you to read this. He then leaves you alone in the room.

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Think Simple

When thinking about the entire question to solve, you cannot figure out a direct solution. Instead, you decide to focus on a simpler part of the code challenge. The part you are aiming to solve now is the generation of the text to indent the folders of the various levels. After thinking a few minutes, you believe that it would be a good idea to have a function tab(t) taking an integer as an input and returning a text with the correct number of dots. As an example, the evaluation of tab(3) should return "......".

You keep working on this idea and produce the below code.

function tab(t) {
  if (t < 1) return "" 
  return ".." + tab(t - 1)
}

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Solution

After 90 minutes, Orolo comes back to the room and ask you how it went. You discuss with him the question and mention how you tried to solve it. Orolo listen carefully about your code design. He says that he has with him one potential solution to the challenge. He shows it and you both start comparing it with your solution.

function show(f) {
  showCalc(f, 0)
}

function showCalc(f, i) {
  console.log(tab(i) + f.name)
  f.files.forEach(a => console.log(tab(i + 1) + a))
  f.subfolders.forEach(a => showCalc(a, i + 1))
}

function tab(t) {
  if (t < 1) return "" 
  return ".." + tab(t - 1)
}

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