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Many hard LeetCode problems are easy constraint problems

buttondown.com

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Re: Many hard LeetCode problems are easy constraint problems

#71
post #62

SAT, SMT, and constraint solvers are criminally underutilized in the software industry. We need more education about what they are, how they work, and what sorts of problems they can solve.

In what way? They're useful for toy problems like this but they're very slow on larger problems.

Re: Many hard LeetCode problems are easy constraint problems

#72

Earlier quoted context omitted.

If someone solves a leetcode hard with a constraint solver and you don't hire them, you are an idiot. Do you know how few people in this world even know what a constraint solver is, let alone how to correctly define the problem into one? I used a constraint solver to solve a homework problem once in my CS degree 3rd year. My god just writing the damn constraints was a huge cognitive load!

> If someone solves a leetcode hard with a constraint solver and you don't hire them, you are an idiot. I do hope you're exagerating here, but in case you aren't: this is an extremely simplistic view of what (software) engineers have to do, and thus what hiring managers should optimize for. I'd put "ability to work in a team" above "raw academic/reasoning ability" for the vast majority of engineering roles, any day.…

OK, but obviously this presupposes a job where the hiring process is focused on leetcode.

Re: Many hard LeetCode problems are easy constraint problems

#73
post #45
post #5

Great insight. But this is sadly not applicable to interviews. > It's easy to do in O(n^2) time, or if you are clever, you can do it in O(n). Or you could be not clever at all and just write it as a constraint problem This nails it. The point of these problems is to test your cleverness. That's it. Presenting a not-clever solution of using constraint solvers shows that you have experience and your breadth of knowledg…

>The point of these problems is to test your cleverness. In my experience, interviewers love going to the Leetcode "Top Interview 150" list and using problems in the "Array String" category. I'm not a fan of these problems for the kind of jobs I've interviewed for (backend Python mostly), as they are almost always a "give me a O(n) runtime O(1) memory algorithm over this array" type challenge that really doesn't rese…

Interviews should not be about cleverness. They should test that you can code. I almost never write an algorithm because all the important algorithms are in my standard library already. Sure back in school I did implement a red-black tree - I don't remember if it worked, but I implemented it: I can do that again if you need me to, but it will take me several days to get all the details right (most of it looking up how it works again). I use red-black trees all the time, but they are in the language.

You need to make sure a candidate can program so asking programing question make sense. However the candidate should not be judged on if they finish or get an optimal or even correct answer. You need to know if they write good code that you can understand, and are on a path that if given a reasonable amount of time on a realistic story would finish it and get it correct. If someone has seen the problem before they may get the correct answer, but if they have not seen it they won't know and shouldn't expected to get the right answer in an hour.

Re: Many hard LeetCode problems are easy constraint problems

#75

I feel like if I'm being asked this in an interview, they're not asking me to use a constraint solver, they're asking me to _write_ a constraint solver. Just for a specific constraint problem, not a more general constraint solver.

You're right, but that just shows how fundamentally silly this interview approach is. In any real engineering situation I can solve 100% of these problems. That's because I can get a cup of coffee, read some papers, look in a textbook, go for a walk somewhere green and think hard about it... and yes, use tooling like a constraint solver. Or an LLM, which knows all these algorithms off by heart! In an interview, I cou…

I was told to use ANY language in an interview. I asked them if they were sure, so I solved it with J. They were not too pleased and asked me if I could use another language, so I did prolog and we moved on to the next question. Then the idiot had the audacity to say I should not use "J and Prolog" but any common known language. I asked if assembly was fine, and they said no. Perhaps python or javascript. I did the rest in python, needless to say I didn't get the job. :-)

Re: Many hard LeetCode problems are easy constraint problems

#76

Earlier quoted context omitted.

Given this consider that LeetCode solving is rarely ever part of your work. So then, what are they selecting for with the habit?

Selecting for people like themselves.

I think this is one of the more true answers but can you be more specific?

Like in race? Like in wealth? Like in defection willingness? Like in corruption?

Asking for a friend who is regularly identified as among the most skilled but feels their career has been significantly derailed by this social phenomenon.

Re: Many hard LeetCode problems are easy constraint problems

#77
My biggest problem with leetcode type questions is that you can't ask clarifying questions. My mind just doesn't work like most do, and leetcode to some extent seems to rely on people memorizing leetcode type answers. On a few, there's enough context that I can relate real understanding of the problem to, such as the coin example in the article... for others I've seen there's not enough there for me to "get" the question/assignment.

Because of this, I've just started rejecting outright leetcode/ai interview steps... I'll do homework, shared screen, 1:1, etc, but won't do the above. I tend to fail them about half the time. It only feels worse in instances, where I wouldn't even mind the studying on leetcode types sites if they actually had decent explainers for the questions and working answers when going through them. I know this kind of defeats the challenge aspect, but learning is about 10x harder without it.

It's not a matter of skill, it's just my ability to take in certain types of problems doesn't work well. Without any chance of additional info/questions it's literally a setup to fail.

edit: I'm mostly referring to the use of AI/Automated leetcode type questions as a pre-interview screening. If you haven't seen this type of thing, good for you. I've seen too much of it. I'm fine with relatively hard questions in an actual interview with a real, live person you can talk to and ask clarifying questions.

Re: Many hard LeetCode problems are easy constraint problems

#78
post #5

Great insight. But this is sadly not applicable to interviews. > It's easy to do in O(n^2) time, or if you are clever, you can do it in O(n). Or you could be not clever at all and just write it as a constraint problem This nails it. The point of these problems is to test your cleverness. That's it. Presenting a not-clever solution of using constraint solvers shows that you have experience and your breadth of knowledg…

Bottom up dynamic programming algorithms require some cleverness.

All of the ones listed can be solved with a top down dynamic programing algorithm. Which just means "write recursive solution, add caching to memoize it".

For some of these, you can get cleverer. For example the coin change problem is better solved with an A* search.

Still, very few programmers will actually need these algorithms. The top thing we need is to recognize when we accidentally wrote a quadratic algorithm. A quick scan of https://accidentallyquadratic.tumblr.com/ shows that even good people on prominent projects make that mistake on a constant basis. So apparently being able to produce an algorithm on the test, doesn't translate to catching an algorithmic mistake in the wild.

Re: Many hard LeetCode problems are easy constraint problems

#79
post #24
post #5

Great insight. But this is sadly not applicable to interviews. > It's easy to do in O(n^2) time, or if you are clever, you can do it in O(n). Or you could be not clever at all and just write it as a constraint problem This nails it. The point of these problems is to test your cleverness. That's it. Presenting a not-clever solution of using constraint solvers shows that you have experience and your breadth of knowledg…

When I interview with problem solving problems, the point is to understand how the candidate thinks, communicates, and decomposes problems. Critically, problem solving questions should have ways to progressively increase and decrease difficulty/complexity, so every candidate "gets a win" and no candidate "dunks the ball". Interviewers learn nothing from an instant epiphany, and they learn next to nothing from someone…

Would a good answer be "I can do it as a constraint problem, but since I guess you are not asking for this, the solution is..." and then proceed as usual?

Re: Many hard LeetCode problems are easy constraint problems

#80
post #40
post #24

Earlier quoted context omitted.

When I interview with problem solving problems, the point is to understand how the candidate thinks, communicates, and decomposes problems. Critically, problem solving questions should have ways to progressively increase and decrease difficulty/complexity, so every candidate "gets a win" and no candidate "dunks the ball". Interviewers learn nothing from an instant epiphany, and they learn next to nothing from someone…

> the point is to understand how the candidate thinks, communicates, and decomposes problems. 100% and it's a shame that over time this has become completely lost knowledge, on both sides of the interview table, and "leetcode" is now seen as an arbitrary rote memorization hurdle/hazing ritual that software engineers have to pass to enter a lucrative FAANG career. Interviewees grind problems until they've memorized ev…

If somebody writes the optimal algorithm that should be a negative unless their resume indicates they are writing that algorithm often. The only reason you should know any algorithm well enough to get it right is if your job is implementing the optimal version for every single language. Of course nobody maintains one algorithm in many different languages/libraries (say libc++, python, rust, ada, java - each has different maintainers), so I can safely safe the number is zero who should be able to implement your cleaver algorithm. Now if your cleaver algorithm is in the language standard library (or other library they often use) that should be able to call/use it, though even then I expect them to look up the syntax in most languages.
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