# Questions tagged [fastest-code]

The winner of a fastest-code challenge is determined by the runtime performance of the submissions. For fairness, all submissions should be benchmarked on the same machine, which usually means all submissions have to be tested by the host of the challenge. For scoring by asymptotic time complexity, use [fastest-algorithm] instead.

133 questions
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### Experiment Design [closed]

Background I’ve had to make some of these by hand for a science experiment and was checking to see if anybody had any clever ways of achieving this. It feels like sudoku, but not quite. figuring ...
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### Check if all vowels exist in pairs of strings [closed]

Your program should find the number of string pairs (pairs of 2) that contain all vowels (a e i o u), when given an integer N and ...
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### Prime containment numbers (speed edition)

This is sequence A054261 The $n$th prime containment number is the lowest number which contains the first $n$ prime numbers as substrings. For example, the number $235$ is the lowest number ...
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### Arbitrary Randomness (Speed edition)

Given integer n, calculate a set of n random unique integers in range 1..n^2 (inclusive) ...
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### Find arrays with distinct subarray sums

Consider an array A of length n. The array contains only integers in the range 1 to ...
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### Count arrays that are really unique

This is a follow up to Count arrays that make unique sets . The significant difference is the definition of uniqueness. Consider an array A of length ...
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### Fastest algorithm to output array containing all integers in range excluding duplicate digits

Input is a single integer in ascending digit order. The only valid inputs are: 12 123 1234 ...
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### Count arrays that make unique sets

This question has a similar set up to Find an array that fits a set of sums although is quite different in its goals. Consider an array A of length ...
564 views

### Block partition a string

Inspiration. Consider a list l, consisting of numbers. Define a block operation at index i on the list ...
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### Delete some bits and count

Consider all 2^n different binary strings of length n and assume n > 2. You are allowed ...
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### Permutations such that no k+2 points fall on any polynomial of degree k

Description Let a permutation of the integers {1, 2, ..., n} be called minimally interpolable if no set of k+2 points (together ...
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### Calculate the Hafnian as quickly as possible

The challenge is to write the fastest code possible for computing the Hafnian of a matrix. The Hafnian of a symmetric 2n-by-2n ...
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### How many draws are there in Quarto?

Introduction This challenge is similar to Project Euler problems. I came up with it because I was playing a deceivingly simple board game and couldn't come up with an efficient solution to answer a ...
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### Biggest square in a grid [closed]

Challenge Given a grid like this, ...
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### The Missing Number - Version 2

Background: This question is a remix of the one that I made previously on this forum. The only difference with this one is: the range is significantly larger, AND dynamic. Details below! Also, I'm ...
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### The Missing Number Revised

Background: I originally posted this question last night, and received backlash on its vagueness. I have since consulted many personnel concerning not only the wording of the problem, but also its ...
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### Build an Electrical Grid

The Challenge There are N cities aligned in a straight line. The i-th city is located A[i] kilometers to the right of the origin. No two cities will be in the same ...
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### Primitive roots density of number

Definition: A number m is called a primitive root of a prime p the condition that the smallest integer k for which p dividies mk-1 is p-1 Your task Given a tuple (a,b) of positive integers, ...
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### Count arrays of periods

The period of a string is the shortest non-zero shift so that the string matches itself, ignoring any parts that overhang. So for example, ...
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### Products that equal a sum and vice versa

A fun pair of equivalences is 1 + 5 = 2 · 3 and 1 · 5 = 2 + 3. There are many like these, another one is 1 + 1 + 8 = 1 · 2 · 5 and 1 · 1 · 8 = 1 + 2 + 5. In ...
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### remove duplicates from array [closed]

You have given an array from which we need to remove duplicates. Rules: First or immediate duplicates gets removed first. Array contains natural numbers ...
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### Fastest tweetable integer factorizer

The task is to find a non-trivial factor of a composite number. Write code that finds a non-trivial factor of a composite number as quickly as possible subject to your code being no more than 140 ...
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### Plant trees in a park - As fast as you can!

This challenge is inspired by this app. The test cases are borrowed from that app. This is a fastest-code challenge, where the objective is to solve the largest test cases in the least amount of time....
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### Tips for Fastest Code challenges [closed]

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 ...
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### Compute OEIS A005434

The task is to compute OEIS A005434 as quickly as possible. Consider a binary string S of length n. Indexing from ...
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### Roll to see all sides!

Let's say you have a 20-sided die. You start rolling that die and have to roll it a few dozen times before you finally roll all 20 values. You wonder, how many rolls do I need before I get a 50% ...
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### Finding approximate correlations

Consider a binary string S of length n. Indexing from 1, we can compute the Hamming ...
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### Fastest Approximate Common Divisor

Overview In this challenge, you will be given two numbers which are both a small offset larger than a multiple of a medium-size number. You must output a medium-sized number that is almost a divisor ...
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### Count the number of Hamming distance sequences

The Hamming distance between two strings of equal length is the number of positions at which the corresponding symbols are different. Let P be a binary string of ...
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### Count how many distance sequences are far from all others

The Hamming distance between two strings of equal length is the number of positions at which the corresponding symbols are different. Let P be a binary string of ...
168 views

### Google search result short summary [closed]

Intro When you search in google, it always shows you a result with a sample text from the found webpage. For example if you search for "Madonna greatest vinyl", google will show you one line link, ...
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### Generalization of Eight Queen Puzzle [closed]

Here's one generalized version of the famous Eight Queen's Puzzle: Given an n × n chess board, and an integer ...
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### Fastest Home Prime Generator

What is a home prime? For an example, take HP(4). First, find the prime factors. The prime factors of 4 (in numerical order from least to greatest, always) are 2, 2. Take those factors as a literal ...
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### The Tax Historian

Introduction There is a tax collector that has some trouble managing the taxes of his kingdom: the historical records have burnt down in a great fire. He wants to find out how many possible pasts ...
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### Fastest Mini-Flak Quine

Mini-Flak is a subset of the Brain-Flak language, where the <>, <...> and [] ...
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### Read a crossword with a twist!

Similar to this question, but this is a crossword variation! Instead of only one letter per grid square, you can have one or two. Input: A 2d array, or whatever works in your language. You can ...
3k views

### Calculate the permanent as quickly as possible

The challenge is to write the fastest code possible for computing the permanent of a matrix. The permanent of an n-by-n matrix ...
365 views

### Help the poor Cryptographers - DLP Edition

Introduction and Motivation I'm mainly active on Cryptography.SE and as such have already stumbled across the question: "How the hell am I supposed tools like cado-nfs to do stuff!?". They are super-...
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### The fastest square root calculator

Write a program which outputs the square root of a given number in the shortest time possible. Rules It may not use any builtins or powering with non-integers. Input format as a function argument ...
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### Compute the maximum number of runs possible for as large a string as possible

[This question is a follow up to Compute the runs of a string ] A period p of a string w is any positive integer ...
556 views

### Find all the Solutions to this Number Puzzle in the Shortest Time Possible

History My company sends out a weekly newsletter to everyone within the company. Included in these newsletters is a riddle, along with a shoutout to whomever in the company was the first to email/...
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### Quickly express a number with only 0-9 and the four operations, plus one more extra

Explanation Befunge is a two-dimensional program that uses stacks. That means, to do 5 + 6, you write 56+, meaning: ...
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### Approximating a special case of the Riemann Theta function

This challenge is to write fast code that can perform a computationally difficult infinite sum. Input An n by n matrix ...
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### Tic-tac-toe with only crosses as quick as possible

As per Luke's request and Peter Taylor's addition to this challenge. Introduction Everyone knows the game tic-tac-toe, but in this challenge, we are going to introduce a little twist. We are only ...
953 views

### Find the longest path, avoiding obstacles in a 2D plane

The Scenario You are given a matrix of size m x n (width x height) with m*n spots where there are a few obstacles. Spots with obstacles are marked as 1, and those without are marked as 0. You can ...
295 views

### Reproportioning a population by adding fixed sized groups

Introduction Say you have a population of people. This population is made up of 100 Alices and 25 Bobs. So, 80% of the population are Alices and 20% are Bobs. We want to change the proportional ...
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### Calculate the number of primes up to n

π(n) is the number of primes less than or equal to n. Input: a natural number, n. Output: π(n). Scoring: This is a fastest-code challenge. Score will be the sum of times for the score cases. I ...
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### Counting orthogonal circulant matrices

Two rows of a matrix are orthogonal if their inner product equals zero. Call a matrix with all rows pairwise orthogonal an orthogonal matrix. A circulant matrix is one where each row vector is rotated ...