This challenge is intended to be solved by using, manipulating, accepting as input, or outputting numeric values.
21
votes
24answers
2k views
The plus-minus sequence
The plus-minus sequence
The plus-minus sequence is one that starts with two seeds, a(0) and b(0). Each iteration of this sequence is the addition and subtraction of the previous two members of the ...
18
votes
3answers
163 views
Highest score on the field
Introduction
Let a field be a rectangle filled with only the characters - and [0-9]. An example of a field is:
11-011123
111-010--
0010---01
111-01234
You see that this field has been separated ...
21
votes
5answers
595 views
Commutation of 27 functions
Introduction
Let's define a ternary function as a function from the three-element set S = {0,1,2} to itself: it associates to each element of S another element of S.
One example of a ternary function ...
17
votes
12answers
616 views
Equality in the sum of digits
Introduction
Let's take the number 180. This is an interesting number because the sum of digits of this number is equal to:
1 + 8 + 0 = 9
And the squared version of this number, or:
180² = 32400 ...
12
votes
3answers
403 views
How many sides does this polygon have?
So in 1st grade math, you learn the names of polygons. Three sides is a triangle, 4 is a square, and 5 is a pentagon. However, in 1st grade honors, you go a bit further.
Your challenge
There is a ...
-2
votes
16answers
340 views
Print all the numbers! (At least, as many as possible.) [closed]
Your task is to print a number. Simple, right? It is simple, but not as simple as this. The first answer is to print the number 1, the second answer is to print the number 2, etc.
Rules
The first ...
29
votes
34answers
3k views
Yahtzee Small Straight Detection
In the game Yahtzee, players roll five six-sided dice, and attempt to create certain hands to score points. One such hand is a small straight: four consecutive numbers, not necessarily in order. The ...
36
votes
35answers
4k views
Making a coin fair
You have a coin that produces 0 or 1. But you suspect the coin may be biased, meaning that the probability of 0 (or 1) is not necessarily 1/2.
A well known procedure to "transform" a biased coin into ...
19
votes
0answers
197 views
Cycles in run-length encoding
Consider some binary sequence, using 1 and 2, e.g.:
1, 2, 1, 1, 2, 2, 1, 2, 1, 2, 2, 1 ...
Let's write down the run lengths of that:
1, 2, 1, 1, 2, 2, 1, 2, 1, 2, 2, 1 ...
_ _ ____ ____ _ _ ...
10
votes
4answers
952 views
The Unholy numbers
This challenged is highly inspired by what @Mego created with his Holy and Holier numbers, lots of thanks to him and his puns.
Holy numbers are numbers composed of only the digits with holes, which ...
7
votes
1answer
170 views
Leaping Lizards!
Suppose we define a simple program that takes an array L of natural numbers with some length N and does the following:
i=0 #start at the first element in the source array
P=[] ...
5
votes
2answers
219 views
Chaotic Number Shuffling
You have a deck of cards, consisting of cards with non-negative numbers on them, and you haven't shuffled it yet, and no player trusts the other players to be fair at shuffling. You devise a way to ...
20
votes
9answers
820 views
Highly composite numbers
A highly composite number is a positive integer that has more divisors than any smaller positive integer has. This is OEIS sequence A002182. Its first 20 terms are
1, 2, 4, 6, 12, 24, 36, 48, 60, ...
16
votes
20answers
600 views
Descending digit sequences
Introduction
As an example, let's take the number 7. We then duplicate this and place 7 spaces in between. We get this:
7_______7
After that, we are going to decrease the number, until there are ...
42
votes
12answers
2k views
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 ...
-5
votes
7answers
130 views
Find if a number contains a digit without ever using using its string representation
The Challenge:
Find if a number contains a digit. The number and the digit are to be taken as input. Output must be a boolean value. But you are not allowed to use the string representation of the ...
50
votes
10answers
3k views
Quack the Angry Duck
No one is quite certain what the emoticon >:U is intended to represent, but many scholars believe it looks like an angry duck. Let's assume that's the case.
Task
Given an integer n between 0 and ...
2
votes
1answer
204 views
Implement my method of adding numbers mentally
Note: This challenge has been changed to eliminate the strict whitespace manipulation requirements that made this challenge low-quality. Some rules regarding whitespace have been changed.
I'm ...
21
votes
3answers
310 views
The Holier Numbers
As we learned from The Holy Numbers, there are 5 holy digits (0, 4, 6, 8, 9), and positive integers consisting solely of those digits are holy. Additionally, the holiness of a number is the sum of the ...
15
votes
9answers
420 views
Block-diagonal matrix from columns
Inspired by Copied from this question at Stack Overflow.
Given a matrix A, create a matrix B such that the columns of A are arranged in a block-diagonal fashion. For example, given
1 2 3
4 5 6
the ...
21
votes
9answers
1k views
Generate lazy values
Related: Program my microwave oven. Inspired by Generate lazy microwave input.
The lazy value of the non-negative integer N is the smallest of the integers that are closest to N while all their ...
17
votes
3answers
274 views
Generate lazy microwave input
Related: Program my microwave oven and Generate lazy values.
My colleague is so lazy that he doesn't even bother to move his finger when programming the microwave oven. (This is actually true!)
Help ...
18
votes
1answer
145 views
Sandpile integers
Challenge
You will be given a positive integer n as input. Output should be a pyramid-like sandpile built on the rules specified below:
Each integer "falls" downward from the same initial starting ...
23
votes
31answers
1k views
Adding up the digits and the digits reversed
Given a number > 0, output the sum with all digits (1 .. n) concatenated and reversed and add them up. For example, with n = 6:
The numbers 1 to 6 concatenated:
123456
Reversed:
654321
Adding ...
9
votes
1answer
135 views
Taxi me some numbers
Taxicab Numbers or OEIS A011541 are the least numbers that are able to be represented as n different sums of two positive cubed integers, for successive n.
You'll need to print out the nth taxicab ...
24
votes
8answers
2k views
That's a prime… almost
If you've ever learned about primes in math class, you've probably have had to, at one point, determine if a number is prime. You've probably messed up while you were still learning them, for example, ...
17
votes
13answers
1k views
The middle-square method
Introduction
The middle-square method is used for the generation of pseudorandom numbers. However, this is not a good method in practice, since its period is usually very short and has some severe ...
27
votes
15answers
887 views
Repair the ranges
Given an input of a list of positive integers with some replaced with 0,
output the list with the missing numbers that were changed to 0 replaced.
Characteristics of the input list:
The list will ...
10
votes
1answer
252 views
How many letters in this word?
Inspired by Project Euler #17, this is your challenge. Write a full program or function that takes a number as input, then print or return how many letters it would take to count up to and including ...
45
votes
19answers
5k views
The Holy Numbers
In many fonts (specifically in the Consolas font), 5 out of the 10 decimal digits have "holes" in them. We will call these holy digits:
46890
The 5 unholy digits are thus:
12357
An integer may ...
15
votes
4answers
329 views
Find the missing number in an undelimited string
The challenge is to identify the missing number in a string of undelimited integers.
You are given a string of digits (valid input will match the regular expression ^[1-9][0-9]+$). The string ...
5
votes
3answers
254 views
Output the smallest powers of 2 with two identical sub-strings of digits n long
For each integer n, 0 or higher, output the lowest power of 2 that has two identical sub-strings of n digits in decimal, and the two indices where the digit sub-strings start (0-based).
n ...
18
votes
15answers
1k views
Compute minimax of an array
Inspired by this question
Consider an array x such as [1 5 3 4] and a number n, for example 2. Write all length-n sliding subarrays: [1 5], [5 3], [3 4]. Let the minimax of the array be defined as ...
-3
votes
1answer
93 views
Implement decimal-multiplication modulo
Most people can't easily do modulus (or work out if a number is divisible by another number) in their heads because long division is harder than addition, subtraction and multiplication. The following ...
13
votes
20answers
1k views
Output the juggler sequence
The juggler sequence is described as follows. Beginning with an input a1, the next term is defined by the recurrence relation
The sequence terminates when it reaches 1, as all subsequent terms ...
7
votes
4answers
149 views
Compute overall ranking
You are given a table that represents the rankings of S subjects according to a number C of different criteria. The purpose is to
compute an overall ranking according to a weighted sum of the C ...
15
votes
13answers
867 views
Get the closest value to number
In this code golf, you need to get the closest number from another one in a list.
The output may be the closest number to the input.
Example:
value: (Input) 5 --- [1,2,3] --- 3
And, the program ...
36
votes
56answers
9k views
How even is a number?
The ancient Greeks had these things called singly and doubly even numbers. An example of a singly even number is 14. It can be divided by 2 once, and has at that point become an odd number (7), after ...
16
votes
31answers
802 views
Filter out and add up
Task
The task is very simple. Given a non-empty string containing numbers, uppercase and lowercase letters, output the sum of the remaining numbers. For example:
a1wAD5qw45REs5Fw4eRQR33wqe4WE
...
4
votes
1answer
81 views
Convert to and from the backwards-factorial number base
I wanted to ask this question: Convert to and from the factorial number system but I'm a couple of years too late!
So, instead you must convert to and from the lairotcaf backwards-factorial number ...
12
votes
11answers
2k views
Convert English to a number without built-ins or libraries
This challenge is similar to this other, however I made a restriction (see bold text below) that I think would made it much diffent and (I hope) fun either.
The Challenge
Write a program or a ...
12
votes
6answers
813 views
Number of steps for a binary search
Given an input of a positive integer, output the number of steps it takes to
find the input via a binary search starting at 1.
We are simulating a binary search for the integer that was given as ...
6
votes
3answers
144 views
Inverse Champernowne Substrings
The Champernowne Constant is the irrational number 0.1234567891011... extending ad infinum.
We've done a question about it before. But this question is about its reciprocal, known as the Inverse ...
28
votes
18answers
3k views
Sort by Multiplying
You should write a program or function that given a list of positive integers multiplies each element with the smallest positive integer possible to create a strictly increasing list.
For example if ...
6
votes
1answer
118 views
Implement almost-equals for IEEE numbers
Isn't it annoying when you're working with floating point numbers and your code doesn't work because two numbers are not equal by the least significant bit? Now you can fix that!
Write some code that ...
12
votes
4answers
311 views
All the numbers that fit in a string
Write a program or function that takes in a positive integer N. Output a list of all the distinct decimal numbers that can be written in exactly N characters using digits (0123456789), decimal points ...
20
votes
33answers
3k views
Electrical outlet
This is a problem from NCPC 2005. Roy has
an apartment with only one single electrical outlet, but he has a bunch of power strips.
Compute the maximum number of outlets he can have using the power ...
17
votes
8answers
343 views
Print the Super Collatz numbers
The Collatz Sequence (also called the 3x + 1 problem) is where you start with any positive integer, for this example we will use 10, and apply this set of steps to it:
if n is even:
Divide it by ...
20
votes
17answers
997 views
Rearranging the sequence
Introduction
Let's observe the following sequence (non-negative integers):
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, ...
For example, let's take the first three numbers. These are 0, 1, 2. ...
16
votes
13answers
463 views
Say What You See
The "Look and say" or "Say what you see" sequence is a series of numbers where each describes the last.
1
11 (one one)
21 (two ones)
1211 (one two one one)
111221 (one one one two two ones)
312211 ...
