ICPC World Finals: Ecnerwala vs Errichto Kotlin Match

2 years ago, # |

+224

Somehow I still think that tourist will win

→ Reply

Sahil_32

2 years ago, # |

-9

Wishing everyone positive delta

→ Reply

2 years ago, # |

+17

Can someine explain to me how a language that forces bounds checking on every array access is good for competitive programming? Thank you very much

→ Reply

chromate00

2 years ago, # ^ |

← Rev. 2 →

-29

at least you won't RTE due to OutOfBounds that way

(also JetBrains is an ICPC/Codeforces sponsor as you may already know)

→ Reply

Tutis

2 years ago, # ^ |

+84

It increases the constant factor and forces you to think more to get rid of the extra logs in complexity.

→ Reply

qwerty787788

2 years ago, # ^ |

+100

As someone who uses Rust (which does bounds check on every array access), I can tell it is very good for competitive programming! And I never saw a problem, which is solvable in C++, but Rust gets TL.

As for bounds checking — an understandable failure message is always better than undefined behavior, don’t you agree?

→ Reply

2 years ago, # ^ |

+30

An understandable failure message in a submission does no good at all. For locally ran code, C++ does pretty well on that front: address sanitizer + debug flag(s) give you not just the line number of out of bounds access, but a bit of stack trace and also the line number of the corresponding allocation.

Using the production build for debugging is an error (or self-challenge) of the user, not of the language.

→ Reply

qwerty787788

2 years ago, # ^ |

+42

Getting RE is always better than getting WA. You can look for specific types of errors or generate random tests locally. Much easier to debug.

Btw, do you think most competitive programmers use address sanitizer by default when testing? Anyway, it is much better to get the line number, stack trace, and all other stuff just off the box, without the need to set up the correct flags.

→ Reply

2 years ago, # ^ |

+14

Getting RE instead of WA at the cost of getting TLE instead of AC if your algorithm is not optimal, but would work in an unsafe language

→ Reply

Golovanov399

2 years ago, # ^ |

+13

Okay, don't use it then. There are people who like kotlin/rust/any other programming language for whatever reasons, why are you trying to humiliate their languages?

For example, I like using kotlin, because it makes me feel that it was designed for humans, but that doesn't mean that I will go and laugh at disadvantages of C++ to kotlin

→ Reply

2 years ago, # ^ |

I am not humiliating them, I just challenge their claim that it's a good CP language, for the aforementioned reasons. If a language wants to move in that direction, they should give their users a choice to avoid bounds checking and all other unnecessary stuff.

In my view, a good language for CP should have an unsafe foundation, and the safety we're talking about should always be an abstraction built on top of it, and it should always be optional.

I like that Rust has overflow checks in Debug mode but not in Release. Why not the same logic when accessing arrays?

And yes, there are many things I don't like in C++. Its foundation is great, but its syntax and the standard library are terrible compared to other languages. There should be a langauge designed specifically for CP.

→ Reply

Golovanov399

2 years ago, # ^ |

+10

I mean, most of the problems on codeforces can be done in Kotlin, and in many of them the solution in Kotlin looks clearer than the solution in, say C++ or python because of the tools Kotlin provides (I am not a Kotlin expert, so for me these tools are mostly convenient functions for pretty much anything I want to do with basic objects, and these functions are named so that I can guess that they exist by entering what I want to do in the Idea ide). Yes, I have seen problems that I couldn't do in Kotlin due to time limit, and yes, Kotlin probably does a lot of unnecessary stuff that only slows down my solution while doing nothing useful, but does it really make the language bad for CP? And if it does, have Jetbrains claimed otherwise? Only if they advertise it among competitive programmers, to me that doesn't mean that they claim that it is perfect for competitive programming, but that they are popularizing a young language.

Also, as far as I know, Kotlin indeed was not created for CP, but it had a purpose to be a Java-like kinda functional language, probably for android or anything. Have the idea of creating the ultimate CP language been discussed earlier?

→ Reply

2 years ago, # ^ |

+19

And yes, there are many things I don't like in C++. Its foundation is great, but its syntax and the standard library are terrible compared to other languages. There should be a langauge designed specifically for CP.

D language has nicer syntax for templates and ranges compared to C++. I think that it is very good for competitive programming. D does have arrays bounds checking in debug builds, but omits them in release builds.

There's just one major problem: right now Codeforces offers a pretty bad compiler for D language (a 32-bit DMD). But a 64-bit LDC compiler is necessary to compete on equal footing with C++ and Rust languages.

Gassa or hos.lyric could probably ask Mike to provide a D compiler upgrade.

→ Reply

2 years ago, # ^ |

Anyone that feels humiliated by constructive criticism has bigger problems than competitive programming problems.

My colleagues use Kotlin as a Java alternative and are very happy with it. We also have a C++ engine I'm maintaining. There are no plans to freeze the engine and start using Kotlin for everything new, because performance matters too much and performance critical code tends to be simple enough to implement in C++. These are simply different use cases, which is the norm in software development. Any "my language can do it all better!" claims have been and will be challenged. That's also normal.

→ Reply

Golovanov399

2 years ago, # ^ |

Did I miss Jetbrains stating that "their language can do it all better"? If they had, then I, indeed, misinterpreted the original comment of ivan100sic, and the whole discussion makes more sense to me.

→ Reply

2 years ago, # ^ |

Afaik not literally, but it's been hyped up in that sense, as not just a good Java replacement but good for anything.

→ Reply

Gassa

2 years ago, # ^ |

+36

I'd take that any day.

To me, a solution which is slow but right is worth much more than a solution that is fast but wrong. With a slow solution, I could locate the bottleneck (which is a few percent of the code), and optimize just that. With a wrong solution, the error could be just anywhere in it. In the former case, the way forward is much more deterministic.

A rather common view of a strong competitive programmer seems to be to disregard the human-faced complexity of finding bugs, training themselves to overcome it with their wits and brain. In this view, if you make many bugs, you have to train harder to make less. Yet, a more realistic approach is to embrace that people — including oneself — make bugs, and then look for the features that make them less probable: in the language, tools, coding style, etc. The cost one is willing to pay for that depends on how much they appreciate being helped to code without bugs.

→ Reply

2 years ago, # ^ |

Do you know that your submission 150267074 was likely to TLE if codeforces online judge compiled it with array bounds checking enabled? Should we ask Mike to remove at least the -noboundscheck option from the DMD's command line? But you seemed to be in favour of disabling bounds checking for release builds in your older comment.

→ Reply

Gassa

2 years ago, # ^ |

I debug locally, so no: personally, I'm all in favor of testing the release version in the system, as it is now. It seems against the usual competitive programming guidelines to test debug version when -noboundscheck is available in the language.

For people submitting to debug, such option alongside release build may have been nice, much as we have clang++17-diagnostics option for C++. With the current design of compiler list though, looks like it would be too much clutter anyway.

On the other hand, the "every other language is slower than C[++]" mantra doesn't prevent me from accepting 99% of my solutions in D, even with DMD. With the usual guarantees of having a jury solution (de facto C++) at least 2x faster than TL, it's enough for my language as well, even with a suboptimal compiler and for alternative solutions with the intended complexity.

With DMD compiler, I'm having a hard time trying to accept $$$O(n^2)$$$ instead of $$$O(n \log n)$$$ — where GCC's vectorization capabilities shine — but that's it. Would be fine with GDC or LDC compiler as well.

→ Reply

2 years ago, # ^ |

-8

If you enjoy competing while being artificially handicapped, then I suggest you to try CodeChef. CodeChef's GDC compiler is used without any optimization options at all, which results in a nice 3x-6x performance penalty for those, who are looking for an extra challenge.

Still you are not the only D language user on Codeforces. And not everyone wants to be handicapped. Sometimes DMD is very close to LDC, sometimes it's a complete disaster (LDC: 266 ms vs. DMD: 1337 ms). The DMD performance disadvantage typically averages to 30-40%, but 40% is not the upper bound.

Right now it's difficult to recommend D language to new users when both CodeChef and Codeforces offer suboptimal or badly misconfigured compilers.

→ Reply

Gassa

2 years ago, # ^ |

Sorry, what?..

Let me make this clear.

If Codeforces gets an LDC or GDC compiler, I'd love that.
I don't have a case-in-point to show and tell Mike "see, the current compiler is a complete disaster, here's a better one". Seems like you do — do go on and suggest it!

→ Reply

cyrus_msk

2 years ago, # ^ |

← Rev. 2 →

+18

Obviously I don't have cases too, but I just found one interesting finding: when hos.lyric is solving contests at CF, she uses D for first problems, but for last problems (E,F,...) she is switching to C++. I don't know why — but maybe performance/memory usage could be the issue in those problems for her..

PS Congrats with good results of SPBGU at ICPC

→ Reply

2 years ago, # ^ |

I generate random tests locally independent on what verdict I get.

There's a tiny fraction of situations in which it'll cause a WA instead of RE that's actually leading towards wrong assumptions. Yes, it's a slight improvement in that sense.

There's a lot of such slight improvements but it's very debatable if they're worth focusing on because everything comes with tradeoffs. For example, I can write more cache efficient code automatically now than 4 years ago. What does it give me? Perhaps two more ACs in contest or a bunch of avoided TLEs, but perhaps at the cost of not subconsciously focusing on more important things.

Similarly, every crutch like error messages or sanitizer has a tradeoff of less developing debugging skills and understanding how things work and why they can go wrong the way they sometimes do ("RAII = stack allocation", "return value goes in register" etc). IMO everyone should practice hardcore without debug tools, only compete with them.

In summary, there are big things like learning segment trees that are 100% worth the effort, and lots of tiny ones. You're focusing on one such tiny thing.

Btw, do you think most competitive programmers use address sanitizer by default when testing?

Of course not. Most competitive programmers are complete noobs who know next to nothing. Few people know about optimize/target pragmas, much less sanitizer. Few people can write segment trees too.

Now, however, anyone can read this convo and find out that such a thing exists. We learn as we go, about everything.

just off the box, without the need to set up the correct flags.

Through providing libraries for various real life use cases, I found out very painfully that there's no such thing as off the box. Everything involves a bit of effort at the start. With sanitizer too, it's still just a bit of effort like installing the package containing it and copypasting flags.

→ Reply

Swistakk

2 years ago, # ^ |

"Few people know about optimize/target pragmas, much less sanitizer"

Imho pragmas are some shaman-like weird almost redundant tricks while sanitizers are basic life-saving features I can't imagine participating without

→ Reply

2 years ago, # ^ |

Being able to set things like higher optimisation or vectorisation can be pretty important sometimes. (I vastly prefer function attributes since Ofast on whole code can be disastrous compared to Ofast on 4 nested fixed-size loops, but that's a detail.) I actually haven't been using asan until fairly recently and at that point I don't think it gave me all that much compared to learned skills, just less time wasted. I'm glad I developed those skills, would recommend.

→ Reply

nor

2 years ago, # ^ |

As someone who wanted to increase awareness about pragmas, I agree (both about pragmas and sanitizers). The pragmas are nothing but a way to tell the compiler to use certain flags while compiling the file. They simply turned out to be useful in competitive programming environments because you can't change the compilation flags on your own while submitting, so pragmas become useful in providing some control over the compiler.

By the way, I would like to see this changed in a limited manner on Codeforces (similarly, uploading custom libraries) — configurable compilation flags are very cool, but not without downsides — maybe compilation error or some other verdicts need some specific compiler output or program behavior, and allowing compilation with arbitrary flags could make for a DOS attack, like linking statically against huge shared objects.

I believe everyone who writes code should know some basic stuff about their tools to make their life simpler (especially their compiler and what kinds of debugging features it provides).

→ Reply

2 years ago, # ^ |

They simply turned out to be useful in competitive programming environments because you can't change the compilation flags on your own while submitting

I've actually found pragmas (or attributes, as I said they're more specific) more useful in real software development than competitive setting. It sometimes turns out that you want to disable a warning in part of a code, or go for #pragma once instead of custom header guards, or do simple multiprocessing with openmp... it can be difficult if you're using different compilers for different targets (did you know clang doesn't support optimize() for anything except O0?), but deals with a lot of situations the language didn't handle.

→ Reply

nor

2 years ago, # ^ |

I was mainly referring to optimization pragmas when I wrote that comment, I should have been clearer.

I've used #pragma once and #pragma omp as well, they're pretty useful. Some other uses a lot of people don't know about (but can be useful) are #pragma pack (for underaligning) and diagnostic pragmas (including message, error and warning pragmas). I haven't really used other pragmas (except #pragma GCC ivdep which indicates to the compiler that there are no dependencies that will prevent vectorization of the loop).

→ Reply

chromate00

2 years ago, # ^ |

← Rev. 3 →

+13

an understandable failure message is always better than undefined behavior

On the C++ side, .at(x) actually does check bounds properly, but it's much, much more ugly compared to a pair of square brackets.

→ Reply

lomienyeet

2 years ago, # |

Since competitive programming is a mind sport, will someone setup bets for this match?

→ Reply

snowysecret

2 years ago, # |

+31

arvindf232 vs Errichto when?

→ Reply

Vicfred

2 years ago, # |

Can I live-cast this on my stream in spanish?

→ Reply

Swistakk

2 years ago, # |

Ez W for ecnerwala

→ Reply

Sreedhar3210

2 years ago, # |

Hail Errichto

→ Reply

steinum

2 years ago, # |

+84

both on stage

→ Reply

toulst

2 years ago, # ^ |

← Rev. 2 →

-24

They are doing contest in Dhaka?

→ Reply

steinum

2 years ago, # ^ |

yes, on the stage of icpc

→ Reply

Radewoosh

2 years ago, # |

WA on 1, I agree that it's not worth to install kotlin's compiler/interpreter on your machine just for this one contest and nothing more in the future.

→ Reply

kostka

2 years ago, # ^ |

+30

I said it: stop trying to make Kotlin happen, it's not going to happen.

→ Reply

Radewoosh

2 years ago, # ^ |

+39

Agree. But don't take it wrong jetbrains, you are known for your awesome IDEs, just don't ruin that.

→ Reply

jvmusin

2 years ago, # ^ |

You don't need to install anything when you have IntelliJ, it's already there.

→ Reply

-is-this-fft-

2 years ago, # ^ |

+24

you don't need to install anything if you have already installed this other thing

→ Reply

Radewoosh

2 years ago, # |

+139

You can't run dfs, great advertising xd

→ Reply

elizarov

2 years ago, # ^ |

+27

You cannot run naive dfs in stack (stack size is not big enough by default) but you can easily move it to heap in Kotlin. That requires some more Kotlin knowledge than those guys had and it was not needed in this problem anyway.

→ Reply

Digant_Sheladiya

2 years ago, # |

← Rev. 2 →

→ Reply

bicsi

2 years ago, # |

+70

Ecnerwala vs Errichto vs Kotlin match, can’t wait to see it!

→ Reply

Kano

2 years ago, # |

I really want to see Jiangly vs. tourist too

→ Reply

AlexMari

2 years ago, # ^ |

I hope all wanna see that!

→ Reply

Krantzy

2 years ago, # |

It would be nice to have acces to the code of ecnerwala and Errichto

→ Reply

elizarov

2 years ago, # ^ |

← Rev. 2 →

+55

It'll be open soon. Don't use it, please, as an example of good Kotlin code, though :)

→ Reply

BrynzaMasterZa228

2 years ago, # |

+19

yooo sick 1v1 contests are happening. when will we see boxing ?

→ Reply