Tips for Fastest Code challenges

What general tips do you have for how to answer fastest-code challenges?

Please post one tip per answer.

The objective of these challenges is to make the program that will run in the least amount of wall-clock time given a specific set of computer specifications (based on who will be judging the timings).

Please keep tips specific to fastest-code and not fastest-algorithm; you can assume that the coder has already found the most efficient algorithm to use.

HyperNeutrino

Posted 2017-06-19T05:28:15.623

Reputation: 26 575

Didn't we decide, back on Meta, that this is "too broad"? You could probably host an entire Stack Exchange site about code optimization, rather than just a single question. (In fact, there's a tag on Stack Overflow on the subject which has over 20,000 questions.) EDIT: Right, here's the Meta post in question that supports the close vote.

– None – 2017-06-19T05:55:34.107

@ais523 Hm. I should have checked meta to see why this didn't exist already because it seems like someone should have asked this already. Thanks for the feedback! – HyperNeutrino – 2017-06-19T06:06:32.247

@HyperNeutrino It doesn't quite not exist already: https://codegolf.stackexchange.com/q/50073/8478

– Martin Ender – 2017-06-19T06:07:59.077

@MartinEnder Oh. Right, search doesn't find deleted things. Whoops. – HyperNeutrino – 2017-06-19T06:17:22.713

Related – Beta Decay – 2017-06-19T06:20:22.900

Answers

Language

For example, Python is an interpreted language, not a compiled language, so it would surely be faster if you wrote it in C to begin with.

Rust, C++, C, javascript, and Haskell seem to be popular choices. One would have to evaluate them.

Leaky Nun

Posted 2017-06-19T05:28:15.623

Reputation: 45 011

Hm. I never actually thought about the time wasted by higher-level languages. Nice. – HyperNeutrino – 2017-06-19T05:32:14.687

Swift 3.1 and later with Whole-Module Optimisations or with -O(fast) can be faster that C in some cases, but can be outclassed when doing complex tasks – Mr. Xcoder – 2017-06-19T12:28:18.030

Standard ML is also a decent choice, since MLton is a whole-program optimizing compiler. As far as language design goes, Haskell gets a lot of advantages for being lazily evaluated – musicman523 – 2017-06-19T12:51:23.683

1There's no such thing as an interpreted language. Implementation of a language ≠ the language itself. And Python has alternative implementations, some of them (example—PyPy) are JIT'ed. – Display Name – 2017-07-05T06:08:11.823

Bitwise hacks

In some cases, bit-level hacks can cut a lot of time (especially when working on small enough sets), or for larger sets, std::bitvector in C++ can help as well. Depending on the algorithm, these kind of hacks can improve the running time by a factor than can sometimes be as high as 64^2 (or even higher in some cases I have never encountered).

nore

Posted 2017-06-19T05:28:15.623

Reputation: 436