Questions related to elementary arithmetic.

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21
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19answers
1k views

Interquartile Mean

Task Given (by any means) a sorted floating point dataset, return (by any means and within 1‰ of the correct value) the interquartile mean. One possible algorithm Discard the lowest and highest ...
24
votes
28answers
1k views

Substring Sum Set

Introduction Let's observe this array: [3, 2, 4, 1, 1, 5, 1, 2]. Each element displays the length of the substring which must be summed up. Let's take a look at the first element of the above array: ...
16
votes
64answers
2k views

Divisibility test

Task Given two strictly positive integers n and d as input, determine whether n is evenly divisible by d, i.e., if there exists an integer q such that n = qd. You may write a program or a function ...
13
votes
15answers
3k views

How to weight loss easily?

In this question, we will only focus on losing weight by doing exercise, although there are still many ways to lose weight. Different sports burn different amount of calories. For example, playing ...
31
votes
12answers
2k views

Generate Pascal's Braid

This is Pascal's Braid: 1 4 15 56 209 780 2911 10864 40545 151316 564719 1 3 11 41 153 571 2131 7953 29681 110771 413403 1542841 1 4 15 56 ...
19
votes
17answers
5k views

Dijkstra's Challenge

Presented in honor of APL as an interactive tool turning 50 this year Background Ken [Iverson] presented his paper Formalism in Programming Languages in August 1963 at a Working Conference on ...
9
votes
6answers
194 views

Binary Recurrence Sequences

A binary recurrence sequence is a recursively-defined sequence of the following form: This is a generalization of the Fibonacci (x = 1, y = 2, a = [1, 1], alpha = 1, beta = 1) sequence and the ...
1
vote
3answers
200 views

The fastest square root calculator [closed]

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 numbers between 0 and 1. Input format as a ...
17
votes
10answers
657 views

The Camouflage Color Changing Chameleon Challenge

Chameleon challenges are a bad thing, apparently. Too bad, chameleons are beautiful creatures. Time for a change! As we all know, many chameleons posses a remarkable ability to blend in with their ...
27
votes
29answers
2k views

Is it a sum-free set?

A set is sum-free if no two (not necessarily distinct) elements when added together are part of the set itself. For example, {1, 5, 7} is sum-free, because all members are odd, and two odd numbers ...
1
vote
0answers
94 views

Output the happy primes [duplicate]

Input: n Output: A list of length n, with each element being the nth happy prime. Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the ...
12
votes
63answers
3k views

Given two numbers, output their sum

Input: Two decimal integers. These can be given to the code in standard input, as arguments to the program or function, or as a list. Output: Their sum, as a decimal integer. For example, the input 5 ...
16
votes
24answers
1k views

Calculate the sum of ILD

Input: An integer Output: Sum of the input itself + the length of the input + each individual digit of the item. nr + nr-length + {sum of individual digits} = output For example: Input: 99 ...
9
votes
10answers
744 views

Choose from an existing set of weights to make a target sum

When doing weightlifting, I want to make a specific weight by attaching several plates to a bar. I have the following plates: 6 plates of 1 kg each 6 plates of 2.5 kg each 6 plates of 5 kg each 6 ...
22
votes
14answers
2k views

Simplify a square root

Given a positive integer n, simplify the square root √n into the form a√b by extracting all square factors. The outputted a,b should be positive integers with n = a^2 * b with b as small as possible. ...
10
votes
3answers
272 views

Ways to get to the number

Given the input of the first number and the second number (both positive integers, zero exluded), determine in how many ways could you make the second out of the first, using following actions: +1,+2 ...
18
votes
26answers
2k views

Count Up, Replace, Repeat!

Definition Define the nth array of the CURR sequence as follows. Begin with the singleton array A = [n]. For each integer k in A, replace the entry k with k natural numbers, counting up from 1 to k....
7
votes
4answers
237 views

Count, Replace, Add Up! [duplicate]

Definition Define the nth term of the CRAU sequence as follows. Begin with the singleton array A = [n]. Do the following n times: For each integer k in A, replace the entry k with k natural ...
29
votes
37answers
2k views

Difference of the square of the sum

Find the difference between the square of the sums and sum of the squares. This is the mathematical representation: (∑n)^2-∑n^2 Your program/method should take two inputs, these are your lower ...
30
votes
22answers
2k views

Leyland Numbers

Given a natural number n, return the n-th Leyland number. Leyland Number Leyland numbers are positive integers k of the form k = x^y + y^x Where x,y are integers strictly greater than 1. They ...
2
votes
29answers
4k views

The handshake problem

The handshake problem is the classic problem that for n people in a room, if they all shake hands, what's the total number of handshakes that occur. You code should take an input of any number and ...
7
votes
8answers
482 views

Excludivisible numbers

Given an integer N, output the Nth positive number K with the following property in decimal base: For each digit I at position P of K, the number formed from K by removing the Pth digit (i.e. I) is ...
10
votes
3answers
359 views

A Hundred Squares!

Back to basics... As a teacher at the local primary (grade?) school, you need a way to teach your class their times tables. At your disposal, you have hundred squares and a load of red pens. You need ...
35
votes
28answers
7k views

Weapons of Math Instruction

Last time when I tried to come up with something easy that wasn't a duplicate, it ended up being way too hard.. So hopefully this time it's indeed something newcomers can try as well. Input: An ...
28
votes
15answers
3k views

Turn an Array into a Math Problem

Given a nonempty list of nonnegative integers, consider rewriting it as an arithmetic problem where: A plus sign (+) is inserted between pairs of numbers that increase from left to right (a.k.a. ...
24
votes
22answers
1k views

Sum It Up with a Digital Triangle

Well, sum it down really. Write a program or function that takes in a nonempty list of decimal integers (0-9) and outputs a downward pointing "triangle" of digits with the input list at the top where ...
9
votes
3answers
274 views

Simplify a Date

This is similar to simplifying fractions, but with Dates! The input of your program must be of the form mm/dd For example 3/4 //March 4 12/15 //December 15 1/1 // January 1 We assume that the ...
35
votes
16answers
3k views

Has My Pie Been Bisected?

Write a program or function that takes in a nonempty list of positive integers. You may assume it is input in a reasonable convenient format such as "1 2 3 4" or [1, 2, 3, 4]. The numbers in the ...
16
votes
10answers
775 views

Jam don't add like that

Background Jelly's arithmetic atoms vectorize automatically. In fact, x + y is well-defined whenever x and y are numbers or ragged arrays of numbers. Jelly's source code implements this behavior ...
23
votes
27answers
2k views

Find the smallest number bigger than the input whose digital sum is the input

"Digital sum" refers to the sum of all the digits in a number. For example, the digital sum of 1324 is 10, because 1+3+2+4 = 10. The challenge is to write a program/function to calculate the ...
20
votes
28answers
3k views

24 and 12 Hour Times

Write a program or function with no input that prints or returns this string of 24-hour and 12-hour times: 00:00 12:00am 01:00 1:00am 02:00 2:00am 03:00 3:00am 04:00 4:00am 05:00 5:00am 06:00 6:...
-2
votes
2answers
155 views

Restricted average (arithmetic mean) – i.e. without obvious built-ins [closed]

Introduction The arithmetic mean is defined as being equal to the sum of the numerical values of each and every observation divided by the total number of observations. Symbolically, if we have a ...
6
votes
6answers
178 views

Find how many pair elements sums up to N [closed]

Based on a recent question in StackOverflow Write a program/function that takes in one ARRAY/list and returns the number of pair-values which sums up to a given TOTAL. Explaining TOTAL=4, ARRAY=[1,...
42
votes
27answers
3k views

How many steps does it take from n to 1 by subtracting the greatest divisor?

Inspired by this question over at Mathematics. The Problem Let n be a natural number ≥ 2. Take the biggest divisor of n – which is different from n itself – and subtract it from n. Repeat until ...
4
votes
6answers
479 views

Traveling on a flat Earth

Coordinates in the flat-Earth world consist of latitude (x) and longitude (y), which are integers in the range 0...9999. Much like Gaussian integers, but they are always written using this notation: ...
14
votes
15answers
923 views

Find the n-th perfect power!

A perfect power is a number of the form a**b, where a>0 and b>1. For example, 125 is a perfect power because it can be expressed as 5**3. Goal Your task is to write a program/function that ...
6
votes
17answers
344 views

Find the positive divisors!

Definition A number is positive if it is greater than zero. A number (A) is the divisor of another number (B) if A can divide B with no remainder. For example, 2 is a divisor of 6 because 2 can ...
30
votes
33answers
3k views

Compute the Adler-32 checksum

Background Adler-32 is a 32-bit checksum invented by Mark Adler in 1995 which is part of the widely used zlib library (also developed by Adler). Adler-32 is not as reliable as a 32-bit cyclic ...
9
votes
7answers
289 views

Find the repetend of the decimal representation!

In this challenge 2 years ago, we found the period of a unit fraction (1/n where n is a natural number). Now, your task is to write a program/function to find the repetend of a unit fraction. The ...
8
votes
6answers
449 views

Calculate the Kronecker sum of two matrices

In the examples below, A and B will be 2-by-2 matrices, and the matrices are one-indexed. A Kronecker product has the following properties: A⊗B = A(1,1)*B A(1,2)*B A(2,1)*B A(2,2)*B ...
8
votes
3answers
282 views

One-to-one correspondence between pairs of integers and the positive integers

It is well-known that there are one-to-one correspondences between pairs of integers and the positive integers. Your task is to write code defining such a correspondence (by defining a pair of ...
8
votes
8answers
334 views

m-nomial coefficient

While binomial coefficient is the coefficient of (1+x)**n, m-nomial coefficient is the coefficient of (1+x+x**2+...+x**(m-1))**n. For example, m(3,5,6) is the coefficient of x**6 in the expansion of (...
7
votes
9answers
608 views

How many minimum days will he take to complete N units of work?

A person has to complete N units of work; the nature of work is the same. In order to get the hang of the work, he completes only one unit of work in the first day. He wishes to celebrate the ...
15
votes
34answers
2k views

Sum the odd square numbers less than N

Write a program or function to output the sum of the odd square numbers (OEIS #A016754) less than an input n. The first 44 numbers in the sequence are: 1, 9, 25, 49, 81, 121, 169, 225, 289, 361, 441,...
6
votes
2answers
281 views

Federal income tax calculator for procrastinators

Today is Tax Day! Oops. Well, today is tax day if you are a resident of Maine or Massachusetts. So you're probably still completing your return and need a calculator for when you get to Line 44. ...
10
votes
7answers
421 views

Convert to Roman Numeral!

Your task is to convert a given positive integer from Arabic numeral to Roman numeral. Things get difficult when you count to 4000. The romans did this by adding a line above a symbol to multiply ...
20
votes
14answers
886 views

Generate the minimal remainder sequence

Every number can be represented using an infinitely long remainder sequence. For example, if we take the number 7, and perform 7mod2, then 7mod3, then 7mod4, and so on, we get 1,1,3,2,1,0,7,7,7,7,.......
2
votes
3answers
255 views

Solve a quadratic equation using Vieta's formulas

Exposition Your mathematics teacher is a big fan of Vieta's formulas, and he believes that you should use them to solve quadratic equations. Given the equation ax^2 + bx + c = 0 the product of its ...
25
votes
39answers
2k views

Greatest Common Divisor

Your task is to compute the greatest common divisor (GCD) of two given integers in as few bytes of code as possible. You may write a program or function, taking input and returning output via any of ...
21
votes
27answers
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 ...