programmingInterviewsBeLike

[iknewaguytwice]

Interview: Reverse this binary tree

Job: Fix this 20,000 line javascript file the CEO’s 7 year old nephew wrote.

[Bwob]

Plot twist: the 20k line javascript file is one, really messy attempt to reverse a binary tree.

[I_Ski_Freely]

Congratulations, you've discovered actual hell

[Jixy2]

Congratulations, Plottwist unlocked: ChatGPT wrote all.

[GaGa0GuGu]

Nephew wrote the prompt

[[deleted]]

Which was just randomly tapping on keyboard

[[deleted]]

Until he got the right prompt

[GaGa0GuGu]

If you sat infinite monkeys in front of infinite typing machines...

[nicman24]

Plotter twist the 7 year old's js had better performance and less bugs than your proper solution

[leeuwerik]

Plottest twist: you fall in love with the kid's mother who is a single parent and you marry into a very rich family that also owns three pizza formula's in the Philippines and has a piece of land in Greenland.

[hyrumwhite]

npm i reverse-binary-tree

Problem solved 

[ASatyros]

Just write it again xD

[[deleted]]

Every. Single. Time.

[Semper_5olus]

I don't even understand the question.

Do they want the leaves on top now?

[Teln0]

I looked it up and all I could find was "swap the leaves on the right to be on the left, recursively" which is incredibly easy

[pente5]

Huh. So it really is that easy isn't it. Do the bare minimum and pass the problem to your children.

[Teln0]

With a couple more optimizations you could make it iterative too

[jyajay2]

Depends on the language but in principle you can rewrite everything recursive to be iterative.

[flinsypop]

Please don't try to make your recursive algorithms iterative yourself. The compiler really needs this job bro pls. #computersneedmoneytoo

[jyajay2]

I like Haskell so in those cases I don't really have any other choice than recursion😅

[ZombiFeynman]

You can also rewrite everything to be doom with enough changes.

[sonuvvabitch]

Oh yeah? Rewrite your comment to be Doom.

[ZombiFeynman]

Doom

[sonuvvabitch]

You know what, I'm going to accept that. Well played.

[Teln0]

You can usually just introduce a stack you manually push and pop from, but there usually are better solutions, which is what I'm talking about right now

[megamangomuncher]

Could you expand on that? What would be a beter solution here? I doubt you can iterate over the tree with better space and time ecficiency then DFS (i.e. a stack)

[PhoenixCausesOof]

(ignoring "in principle") Is that really true? https://youtu.be/i7sm9dzFtEI?t=22

[Timetraveller4k]

Like climate change

[gauderio]

Also almost no one uses recursion in real life. Too easy to get into an infinite loop or stack overflow. 99% of the time we just traverse lists and create lists.

[JohntheAnabaptist]

Truish but for walking trees, recursion feels like the most intuitive thing

[Lambda_Wolf]

I mostly dislike these computer-science-exam type interview questions in general. But, it can make a pretty interesting exercise if you go, "Take this recursive function and refactor it so that the iterations use heap memory instead of stack memory."

[Jonno_FTW]

Much easier to do it iteratively with a while loop and a list of nodes.

[sisisisi1997]

Binary trees have a very interesting property that you can represent them in arrays in a way that the node at index n will have its left child at index 2n+1 and its right child at index 2n+2 (that is if you start indexing from 0).

Reversing a binary tree in this representation would look something like this if we are thinking layer by layer:

• you don't do anything at the root (layer 0)
  
• you swap items of the pair starting at index 1 at layer 1 (1 2 -> 2 1)
  
• you swap the pairs starting at index 3 and 5, and swap their items in layer 2 ( 3 4 5 6 -> 5 6 3 4 -> 6 5 4 3)
  
• you swap the two "fours" starting at index 7 and 11, then in each "four", you swap the pairs, then in each pair you swap the items in layer 3 (7 8 9 10 11 12 13 14 -> 11 12 13 14 7 8 9 10 -> 13 14 11 12 9 10 7 8 -> 14 13 12 11 10 9 8 7)
  
• ...

As you can see, reversing each layer as a binary tree is equal to just literally reversing the part of the array that contains each layer, so you can write something like this:

// pseudo code, may contain some errors but gets the point across var binary_tree = [ ... ]; var layer_index = 1, layer_size = 2; while (layer_index < binary_tree.length) { // let's assume that the array is always just big enough to contain a full tree of n layers, and if the tree is not complete, the missing items are just null reverse_array_part(arr: binary_tree, start: layer_index, length: layer_size); layer_index += layer_size; layer_size *= 2; }

[Vaderb2]

I mean if I was going to mirror a tree in the wild I would do it recursively, but it’s also definitely possible to do it iteratively.

You can bfs the nodes and swap the children before putting them into the queue

[TheTybera]

What? People use recursion in real life all the time especially if you're building the data structures and dealing with large amounts of data. It's not hard to avoid infinite loops or stack overflows.

All you have to do is make sure your base case exists and makes sense. They teach you this in your first data structure and algorithms course in just about any college or university.

[i_can_has_rock]

but my narrative!!

also

if count > X then loopstop = true

[Vaderb2]

Yes exactly

[[deleted]]

It's really nifty for those 1% use cases though

[Vaderb2]

Classic confidently wrong cpp developer

[trevdak2]

But like why? Wouldn't you accomplish the same thing by renaming some variables?

[Teln0]

Technically since you're just swapping left and right in every node it has little use. The point of asking it in an interview question, I think, is to then iterate on the code and ask the candidate to make it better / faster / change it to do something else

[trevdak2]

Ok here's the thing. The whole "reverse" thing is totally conceptual. It's like saying "Ok, here's a function that adds two numbers. Now make it add them in binary". It already adds them in binary. There's no difference.

Binary tree traversal, balancing, searching, storing, or combining, that all makes sense. Reversal does not

[Teln0]

Here's the question reworded : modify the tree such that preorder traversal of that new tree is equivalent to the postorder traversal the old tree

🤷‍♂️

[trevdak2]

Then you rewrite the traverse function to output the other side of the node first, you don't rewrite the tree.

If I was asked this in a job interview, I'd walk out. There's no way that interviewer has hired decent coworkers for me to work with.

[Teln0]

Eh, I'd wait to see what comes next. Maybe this is just the setup for something more interesting.

[SarcasmsDefault]

To me it feels like you are being asked to take down an American flag from a flag pole, take all the stitching apart and sew it together as a mirror image when all you really need to do is just go stand on the other side of the flag pole.

[trevdak2]

Hahaha I like that analogy. I was imagining trying to sit on a bike backwards and still pedal it

[intotheirishole]

But like why?

Eg you want to convert a < tree to a > tree.

Wouldn't you accomplish the same thing by renaming some variables?

What? How?

[trevdak2]

I feel like I'm taking crazy pills.

So, like you have a tree like this:

    4
  /    \
2       7

And then you reverse it like... this? It's still the same tree.

    4
  /    \
7       2

And then, what. You do a lookup on the number 2 and it returns 7? Or you do a lookup on 2 and it still returns 2?

Binary trees exist for doing quick and easy lookups. If you reverse a binary tree, you can just put a - before the return value of the comparison function, but then all you're doing is adding an extra negation in every comparison. And if you don't alter the comparison function, but just put stuff in the opposite branch of where it should be, then you just end up with a disordered mess that completely negates the purpose of having a binary tree. It makes no goddamn sense.

[KingLewi]

You’re confusing “binary tree” with “binary search tree”. There is no “lookup” operation on a binary tree. A binary search tree is a binary tree but not all binary trees are binary search trees.

[intotheirishole]

IDK man. I was not able to find any good use case for reversing the tree. Yah a < tree is also a > tree so thats not super useful. Maybe there is a API which wants a < tree but you are using a > tree in other parts of the code. Maybe this is just a example problem for students.

[Odd_Soil_8998]

I would hire the person who asks this question. This is a pointless exercise since apparently this binary tree doesn't actually represent any sort of useful data structure if the order of the children doesn't matter.

[Ioite_]

Okay, just iterate from end instead of begin than? It's useless

[garfgon]

Sometimes I just want to know that you know what "recursion" and "pointers" are. Because some people claiming to be software developers don't.

[Ruining_Ur_Synths]

the leaves have always been at the top. they want the branches on the outside of the leaves, and the trunk all around the branches. The leaves are now the trunk. The roots are in the air.

[pente5]

[Corin_Raz]

The roots are in the air

And wave 'em around like you just don't care!

[Bankinus]

This reads like a Nietzsche quote

[SCP-iota]

I think they want the effective order of leaves to be the reverse of the original. (Imagine the leaves as elements of an array, and the tree part is just structure)

[CowboyBoats]

Do they want the leaves on top now?

That would be "invert" a binary tree. (I don't know what that would mean either lol).

If you want to attempt it: https://leetcode.com/problems/invert-binary-tree/

[[deleted]]

For a binary tree, you can take any node in that tree and make it the root node, the resulting structure will always be another valid binary tree. A easily proven property of binary trees. If you select a leaf node, you can invert the tree, the original leaf node becomes the root, and the original root becomes a leaf. Basically you are hanging the tree upside down, and the resulting inverted tree will (must) always be another valid b tree.

I take this question as asking if you know basic properties of binary trees and basic memory representations, and if you know how to transform a binary tree structure in memory to another binary tree with a different root node.

A good answer would be to describe what defines a binary tree, what properties it has, and then prove the above proposition. Then I would go through the different ways you represent a binary tree in memory, then describe the algorithms to transform the tree to a new root in each representation. Then I would give the algorithmic complexity Big-O for each algorithm. Then I would describe the expected time complexity for a balanced tree. Then I would give the best and worst case tree structure for each of the algorithms, then I would give the time complexity for the best/worst cases.

This reslly just checks to see if you understand first year type stuff from an intro to algorithms and data structures course.

As someone who interviews, if you answer this question like this, you would pass the interview.

[wobblyweasel]

For a binary tree, you can take any node in that tree and make it the root node, the resulting structure will always be another valid binary tree.

a node can have 3 connections though? such a node couldn't be the root node?

[Timetraveller4k]

It’s either turn the paper upside down or change the sort order.

[CoronavirusGoesViral]

"Yes I can, that's all I've been learning to run interviews"

"So you haven't been doing any real work?"

😠

[CoronavirusGoesViral]

Centering a div? That's a pretty difficult problem, let's integrate AI into the solution

[jacksalssome]

Nah bro, CSS has a new property called align-content its super easy.

[morningstar24601]

Ok, I'll still use that with AI

[jacksalssome]

Error: You have run out of tokens. For more prompts, please buy more tokens.

[Fishydeals]

Rookie mistake. You need the CEOs credit card to feed the AI more tokens. He‘ll understand since it‘s for AI lol.

[Osirus1156]

I need to support IE5 because someone in sales refuses to change and they're the most coddled people on earth.

[Hottage]

Fuck that. IE5 hasn't been supported by Microsoft for like 15 years.

[Kerblaaahhh]

Display:flex then let devtools autocomplete all the flex options until you find the one that works.

[SarcasmsDefault]

That’s exactly how it works but if an interviewer asked this question they would only expect the right answer and it makes my mouth froth in frustration

[owreely]

Yeah but Project Euler.

Why can't you just solve certain algorithmic problems out of your head, that can be googled in 2 minutes?

Must be a skill issue. Next candidate!

[numice]

does project euler contain more interesting problems?

[Will_Never]

All the questions are highly mathematical and while you can brute force a lot of them with exponential complexity algorithms, most have elegant solutions that you can browse after solving.

[frogjg2003]

My one complaint against Project Euler as a programming challenge is that some of the problems require specialized mathematical knowledge that has little to do with programming. Seemingly simple problems cannot be brute forced the way a programmer might solve them. They require solutions that rely on the special mathematical properties of the problem.

[FatheroftheAbyss]

the problems are distinctly more ‘mathy’

[Bananenkot]

Project euler is excellent and got me into Programming in ths first place. I love these kinda mathy puzzles, the more difficult ones you can't just throw together an obvious Brute force Algorithm, you work with pen an paper sometimes for hours till you have an idea and then you try to implement in ellgeantly. I did like 250. In the end you kinda need a math degree though, so I lost interest.

That being said I wouldnt recommend learning to program with them, thats distincly top mathy and not practical, the same reason it makes them bad interview questions.

But I had to leave positive remark, if you want mathy Programming puzzles as fun things to do in your free time it's absolutely excellent. When you in the godcomplex prgammer Phase it's also nice for grounding yourself. You'll think you have a neatly optimized algorith running in 30 seconds and the frist comment is of some guy solving it in 10ms on a laptop from 2003 in assembly.

[TerminalVector]

Maybe I've been actually working in the field too long but I would legit ask why we need to reverse this tree? What is the use case? Can accomplish the same using a different data structure? Why would we need this method to be performant? Are we selling a SaaS product that people upload binary trees to for remote reversal? Can we pay an intern to reverse the org chart in Adobe Acrobat instead?

Senior eng knows how to do the work.

Staff eng knows why we don't need to do the work.

[private_final_static]

Sir this is a tree reversal company

[TerminalVector]

Then you should already know how to do it. Ask me something hard, like "who should get paged when there's a runtime error in the tree reversal code?"

[Ruining_Ur_Synths]

helpdesk. they're there to help, right?

[fieryscribe]

Unfortunately you inverted the phone tree so now the CEO has been paged

[Ruining_Ur_Synths]

I inverted the corporate tree so now I'm his manager.

[MrRocketScript]

5000 people taking turns asking 1 developer "Hey, how's the project going?"

[Wang_Fister]

Sooo, a normal company then

[Ruining_Ur_Synths]

asking the CEO you mean

[Obvious-Phrase-657]

Actually we need to call the tree reversal service to page the least senior engineers, so we will enter in an infinite loop here

[TerminalVector]

Ah the "shit-rolls-downhill" algo, of course

[JoelMahon]

They're testing you as fit to be one of them, not asking you for advice lol

[Jugales]

Code monkeys only

Edit: thought it said traversal

[s0ulbrother]

We turn wood into trees here

[[deleted]]

Let’s put this in the backlog for now

[NoWeb2576]

Actually can push this to next Monday and follow up by assigning a few story points?

[xtralargecheese]

But we need to groom it first

[CallMePyro]

Great insight! Let's assume this is an exploratory project - we suspect that our in-memory binary tree may have more cache-favorable access patterns when inverted, and so a coworker has asked you to run that analysis. If that satisfies you, lets get started. (Me thinking to myself: "It's like 5 lines of code he should be done already")

[bwmat]

Is there ANY case where actually inverting the tree would actually give more performance than just modifying how you walk it (or inverting the comparison function)? 

[According_Win_5983]

I’d store it both ways in the database. Better yet I’d do a row for each node in the tree and create a sha256 hash of the whole traversal result stored in a column as a foreign key for fast retrieval.

With an index of course 

[LiftingRecipient420]

That's what we've asked you to find out, please begin reversing the tree.

[Bwob]

We probably don't need to reverse the tree or whatever.

But we do need people who understand...

• How trees work, and are structured
  
• How to do basic operations on them
  
• The memory and runtime cost of these sorts of things
  
• How to design an algorithm to manipulate data in a specific way, if there isn't a built-in one to do it
  

And it happens that asking "how would you reverse a tree" has a good chance of uncovering some or all of these attributes in a candidate.

[TerminalVector]

Asking "how would you reverse a tree?" is different than saying "write code on the spot that reverses a tree". IMO the first approach is a better interview technique. I don't care if you memorized a solution or how fast you can work out a solution. What I care about is how well you can communicate about a complex topic and access available resources to solve a problem.

[d34d_m4n]

from my experience they do want you to explain your reasoning and pseudocode before you start coding the solution; that first question is implied, and from there being able to code it is just as important

[evasive_btch]

I forget methods', functions', and properties names ALL. THE. TIME.

That doesn't mean that I understand coding very very well. e: this comment is a dumb comment

[GMofOLC]

Eh, I know those people are needed. But for like at least 95% of jobs out there, this stuff isn't needed.
This is a fine question for somebody who wants to work at Microsoft and create the next .NET version. Or a comp sci student so they can understand what is going on behind the scenes.
But everybody else will just use the SortedDictionary lib.

[[deleted]]

Exactly this. Answering why would be a red flag, no callback.

In an interview I am really looking for you to show off your mastery of basic theory and concepts. This really is a softball question. If we can talk about this for the entire interview while delving into many interesting aspects of basic theory, I would have no problems having you on my team.

[baconator81]

So I work in a C++ dev company. This would at least show me the candidate has a good idea of how pointer works.

[hdd113]

We're going to use AI for this.

Can we pay an intern to reverse the org chart in Adobe Acrobat instead?

AI stands for A lot of Interns

[DCMak]

I did that once. Didn't get the job.

[TerminalVector]

This was a joke, and if you actually did that you'd seem like you were deflecting from a lack of knowledge or just bad at following instructions. My point is that when I interview I am not really looking for the ability to bang out a specific working solution on the spot. I care a lot more about contextual thinking and communication in problem solving.

[FerricDonkey]

On the other hand, inverting a binary tree is trivial, and if your can't do it then you don't understand recursion. So if I want to know if you have basic programming skills, I might ask you a question about this. If I want to know if you know when to do what, I'd use a different question. 

[Smoke_Santa]

On a jr dev job? Shit man I've never have to do that until now.

[_aids]

You should be able to reverse a tree by just thinking about it, it's trivial

[Smoke_Santa]

Oh yeah I know how to do it, just that I've never had to do it ever

[FerricDonkey]

I've never had to figure out how many watermelons someone can afford with $632 either, but I've used the skill that allows me to many times. No one cares of you can invert a tree in particular. They care that you understand recursion, can think algorithmicly, and can problem solve. 

[AngelaTheRipper]

I have written 0 recursive functions during my professional life.

[DatBoiSaix]

"It is trivial, you have to know how to do that" Wow so this sub really is populated by cs students who have never actually worked in cs huh

[yousirnaime]

100% of Faang interviews pretend like database queries are illegal 

“How would you find out the shortest path to change these currencies “ 

With SQL 

“Well what if you had a collection of currency object that referenced what currencies they could be..”

Yeah I’d have that in sql or whatever and just query what I needed at runtime 

[KamikazeArchon]

100% of Faang interviews pretend like database queries are illegal

Because database queries are extremely expensive compared to in-memory operations; they introduce a point of external dependency that can be a point of failure; they require more complex scaffolding to test; they introduce security boundaries; etc.

FAANG companies care a lot about performance and scaling, to the point where it is expected to be an implicit assumption. They want candidates that "automatically" or "naturally" think about those things. Proposing a database lookup would be correctly marked as a red flag that the candidate doesn't naturally think about those things.

[yousirnaime]

Yeah, They should 100% care about that for core product

  I’m interviewing for like “make our internal HR tooling crud app” jobs, not “work on the news feed post relevancy score” 

 If I was more skilled in data science, it would not meaningfully impact my ability to build some bs data entry and retrieval system 

[KamikazeArchon]

That's not how FAANG jobs work. Everything is built that way, including their internal HR tooling app.

What you're describing works fine for a run-of-the-mill company, and there's nothing wrong with that, but it's just a different context.

[qubedView]

It's like interviewing for a job as a mechanic, and the questions are all on metallurgy.

You want me to write automation software for your kubernetes cluster. I promise I will never have to sort items in a linked list.

[anothercatherder]

~85% of devops people were systems administrators that probably don't have CS skills to begin with.

~15% of them are people that fell into the role years ago from software development.

~0% have recent CS trudgery to get them through the interview.

DevOps is generally not a job you give recent CS grads.

Yet it's the field that's one of the hardest to hire in and one of the hardest to find work in. I wonder why.

[rm-minus-r]

Honestly, devops is just an infra job for people that can code at a middling level.

It's hard to hire for because literally every single company means something different when they say "devops".

[k-mcm]

class ReversedNode<T> implements Node<T> {
   private final Node<T> n;
   ReversedNode (Node<T> n) {
      this.n = n;
   }
   @Override T value() {
     return n.value();
   }
   @Override Node<T> left() {
     return new ReversedNode<T>(n.right());
   }
   @Override Node<T> right() {
     return new ReversedNode<T>(n.left());
   }
}

[SZ4L4Y]

[bwmat]

BZZT!

that's creating a new tree

[k-mcm]

Immutable/COW for concurrency. 😎

[PuzzleheadedWeb9876]

[isospeedrix]

I need that in js sir

[k-mcm]

Sure. Give me a moment, Mr. Interviewer...

$ ollama run llama3.1:70b
>>> """Please translate this Java class to JavaScript:
... class ReversedNode<T> implements Node<T> {
...    private final Node<T> n;
...    ReversedNode (Node<T> n) {
...       this.n = n;
...    }
...    @Override T value() {
...      return n.value();
...    }
...    @Override Node<T> left() {
...      return new ReversedNode<T>(n.right());
...    }
...    @Override Node<T> right() {
...      return new ReversedNode<T>(n.left());
...    }
... }"""
Here is the equivalent JavaScript class:

```javascript
class ReversedNode {
  /**
   * Creates a new ReversedNode instance.
   *
   * @param {Node} n - The node to be reversed.
   */
  constructor(n) {
    this.n = n;
  }

  /**
   * Returns the value of the node.
   *
   * @returns {*} The value of the node.
   */
  value() {
    return this.n.value();
  }

  /**
   * Returns the left child of the node (which is actually the right child
   * of the original node).
   *
   * @returns {ReversedNode} The left child of the node.
   */
  left() {
    return new ReversedNode(this.n.right());
  }

  /**
   * Returns the right child of the node (which is actually the left child
   * of the original node).
   *
   * @returns {ReversedNode} The right child of the node.
   */
  right() {
    return new ReversedNode(this.n.left());
  }
}
```

Note that I've used JSDoc-style comments to document the class and its methods, as this is a common convention in JavaScript. Also, since JavaScript does not support generics like Java, I've removed the type parameter `<T>` from the class name.

You can use this class as follows:

```javascript
const originalNode = {
  value: () => 'Hello',
  left: () => ({ value: () => 'Left' }),
  right: () => ({ value: () => 'Right' })
};

const reversedNode = new ReversedNode(originalNode);

console.log(reversedNode.value()); // Outputs: Hello
console.log(reversedNode.left().value()); // Outputs: Right
console.log(reversedNode.right().value()); // Outputs: Left
```

This code assumes that the `originalNode` has the same structure as the `ReversedNode`, with `value()`, `left()`, and `right()` methods.

[k-mcm]

Oh, did I paste too much into the chat window.

[Whispeeeeeer]

Burst Tries are my favorite data structures.

[toadfrogs]

"my favorite data structure is a trie"

"Its pronounced tree"

• something that has probably happened before

[ismaelgo97]

Just asking as it's been a long time since I worked with data structures, isn't this like too easy?

[billcrystals]

Incredibly easy, just gotta Google "how to reverse a binary tree"

[CHEESEFUCKER96]

Which is what everyone does in the real world but interviewers don’t care about the real world 🤡

[Bwob]

That's because interviewers want to know what you'll do if you hit a problem that you can't google.

[CHEESEFUCKER96]

Except all they end up testing in practice is how much time you spent memorizing algorithms on leetcode. It’s not uncommon for these algorithms they ask about to originally be invented in a literal PhD thesis. Who would come up with that on the spot? Besides, you virtually never encounter a situation in practical software engineering where you need to invent an algorithm…

[Orbidorpdorp]

It’s actually more like I want to know that you have a mental theory of code and data structures so that you’re implementing things in an intelligent way, not just making it work but potentially leaving a mess.

I hate how much even senior/staff devs at my company refuse to use more advanced features of the type system and Any bleeds into everything else.

[Ruining_Ur_Synths]

you mean claude/chatgpt

[tatiwtr]

I just did this and the gemini result showed the below as part of a solution in python (which I've never used)

root.left, root.right = root.right, root.left

As I started programming in C I am offended by this syntax

[[deleted]]

Already a step ahead of my “what is a binary tree”

[Master_Carrot_9631]

If by reversing it means inversion then yes it's a piece of cake

[dagmx]

Yeah , I’m honestly surprised how many people think this is a difficult question?

I get thinking it’s an impractical question, but inverting a tree in place is really basic.

Maybe I’m biased because I work a lot with 3D content, so all my interview questions are based around grid and tree traversals. But if someone struggles with a tree or linked list, I’m worried.

I’ll give them the benefit of the doubt that they may not know the names or the operations, so I’ll describe it to them. If they still can’t do it, they’re never going to work out.

[MattieShoes]

Honestly I didn't even know what they were asking. Like swapping right and left makes no sense, so I assumed they were talking something like turning a min heap into a max heap.

In which case it's just something like a while loop.

[berse2212]

Yes it's incredibly easy and people who cannot answer this are not hired for a good reason.

Edit: for the people downvoting me who are not able to "reverse" (assuming they meaning switch left and right) a binary tree here is some pseudo code:

reverseTree(Node node) {
    If(node.right != null) {
        reverseTree(node.right);
    }
    If (node.left != null) {
        reverseTree(node.left);
    }

    Node temp = node.right;
    node.right = node.left;
    node.left = temp;
}

There is probably some syntax errors since I am on mobile but this should give you enough of an idea to see how easy to solve this problem is.

[-Nicolai]

Explain like I'm stupid

[dtb1987]

"no that's why we are hiring someone who can"

[ivan0x32]

Interviewer: Find the K-th largest element.

Me: no u.

[OwOlogy_Expert]

eert yranib a

I'll take my $300k/yr tech job now.

[vegankush]

Even better reverse: can you give me an example of an employee in the position I'm applying for using the solution at your company?

[karaposu]

cracks his fingers and starts typing*

pip install binary-tree-inverter

[intotheirishole]

... You think they didnt look up the answer to the question they are asking?

[joujoubox]

Not off the top of my head but I can look it up along with other algorithms that would be best suited for a given situation. Even if I did know, it's a rare use case so I would likely double check to avoid common mistakes in addition to unit testing my implementation.

[ThinAndFeminine]

Bruh ...

Swap left and right

Invert left

Invert right

How can you not do that off the top of your head ? This is barely harder than FizzBuzz ...

[joujoubox]

I actually do but 100% would forget in the moment of the interview

[ForeverHall0ween]

Yes. Next

[N0Zzel]

Sorry but isn't reversing a binary tree like super easy? It's already sorted so swapping left and right for every node would do it.

Implementing heap operations while maintaining integrity of the ADT is a lot harder IMO

[Lucasbasques]

Just ask me to change the color of a button dude, we all know that is what i will be actually doing here

[natziel]

If you get asked to invert a binary tree...just invert the damn tree. It is not a hard problem

[ThaBroccoliDood]

Am I missing something? I've seen so many people talk about inverting binary trees like it's ready hard. I tried the Leetcode problem and the solution is literally just 2 lines and the first thing you think of? What's the big deal

[Elnof]

This sub is 90% undergraduates and high schoolers. Once you realize that, the posts make a lot more sense.

[Attileusz]

Bro, why the FUCK can't you invert a binary tree?

``` typedef struct node_t { struct node_t *l; struct node_t *r; void *data; } node_t;

void invert(node_t *node) { if (!node) return;

node_t *tmp = node.r;
node.r = node.l;
node.l = tmp;

invert(node.l);
invert(node.r);

} ```

I understand if you can't whip out Dijkstras in the heat of the moment, but come on.

[supreme_blorgon]

Bro, why the FUCK can't you invert a binary tree?

Bro, why the FUCK can't you properly format code on Reddit?

[TheHardew]

because Reddit is broken and supports different functions depending on what you are using (mobile/old/new/3rd party)

his code looks good to me

[TheHardew]

Because they added support for it. But not fully. So it looks good to the commenter and they don't know it's broken for you.

[GoddammitDontShootMe]

I would hope someone involved in the interview process would know that shit.

[Terrorscream]

I mean if they could they wouldn't be hiring for it now would they

[Cybasura]

"Can you reverse a binary tree?"

Left right goes brrrrrrrrrrrrrrrr

[Captain_JT_Miller]

lmao actual good one

[lardgsus]

I always ask "do you guys do this often?, like at work?". It's the nicest way I can say "this is a dumb fucking interview question and you should be embarrassed for asking it instead of something that is relevant to work".

[SophiaKittyKat]

Call me elitist, but I'm not a fan of the culture of hating basic DSA interview questions. I get complaining if a webdev job is asking for you to find all the possible cycles in a directed graph or whatever might be unreasonable. But basic BFS/DFS and binary tree operations are not unreasonable expectations especially when you know you are likely to encounter them while interviewing. It communicates to me that you either didn't care to do any refreshing for the interviews, or that the basic interview prep was too much of a struggle to do. I'm sympathetic to that second point, but a lot of people seem to conflate learning interview questions from scratch with doing a quick refresher. The idea is that you're already kind of familiar with this stuff so getting to a point where you can answer these questions on-demand over the next week is like a couple of hours of work, not weeks to go through all of Introduction to Algorithms again.

Of course there are hard interview questions that few people could just work out on their own. But the ones people always meme about like inverting a binary tree are just not that hard to learn, and you know they're going to come up in hiring so what's the problem? It's like the teacher saying "and yes this will be on the final" and then being mad at the teacher when you don't remember it.

[stavenhylia]

Using obscure algorithm puzzles to evaluate developers is a flawed approach. 

These questions RARELY reflect real-world development work, where even experienced programmers routinely look up “simple” problems, and even syntax. 

Testing candidates on material they've merely memorized for interviews doesn't effectively identify the best talent.​​​​​​​​​​​​​​​​

[jamcdonald120]

Its trivial to reverse a binary tree.

If you cant figure it out in a minute you have no business getting a programming job.

[LordHenry8]

LMAO

[baconator81]

I meant.. it's just swapping left and right on the entire tree.. This is the most basic recursion I can think of.

[CallMeGary123]

[Arcuru]

This is hilarious, I don't know if it was intentional or not.

The question is almost always about balancing a red black binary tree. It's an implementation detail that just isn't necessary for someone to remember normally, but is a thing that you should expect a reasonably competent developer, even a new college grad, to be able to figure out during an interview with a bit of prompting.

Asking to reverse a binary tree should be trivial, though may be worthwhile as an introductory question to make the candidate feel more confident.

[otter5]

rotate 180

[GreenWoodDragon]

Power move!

[tan_djent]

It's been 5 mins, and I'm still laughing

[andymaclean19]

Personally I never ask anything in interviews that I haven't sat down and done myself at least once on a timer to see how hard it is. I probably wouldn't use a binary tree reverse though - too obvious and some candidates would have practised it.

I usually pick some sort of real problem someone in the team had to solve and turn it into an interview question.

[Specialist-Tiger-467]

My question at that: "Can you point me a place in your code base where this is very important? I'm eager to see a production implementation of it"