Introduction Let's define a new arithmetical operation, which I call zipper multiplication. To zipper multiply two nonnegative integers, you add leading zeros to make the lengths match, multiply the corresponding base-10 digits of the numbers, add leading zeros to the results to get 2-digit numb...

Choose any five characters your language supports. There are 5! = 5×4×3×2×1 = 120 ways these can be arranged into a 5-character string that contains each character once; 120 permutations. Choose your characters such that, when each of the 120 strings is run in your language, the 120 outputs prod...

How many cuts are needed to cut a A x B x C cuboid into unit cubes? After each cut you are allowed to rearrange the parts in a way you like, so you may cut several parts in one action. A unit cube is a 1 * 1 * 1 cube. And in a single cut you can move the knife only in one direction. Input The ...

It's holiday season. A mall is empty except of air, money, and a very clever thief that is you. The mall consists of n floors. Each floor can be represented as a rectangular 2D grid. All floors have the same 2D dimensions. You are somewhere inside the building. Your job, as a hard-working thief,...

Given an integer n > 9, for each possible insertion between digits in that integer, insert an addition + and evaluate. Then, take the original number modulo those results. Output the cumulative sum of these operations. An example with n = 47852: 47852 % (4785+2) = 4769 47852 % (478+52) = 152 4...

Write a cross-quine! Choose two programming languages, A and B. You should write two programs: the first one, when run in language A, should output the second one; the second one, when run in language B, should output the first one. As this is code-golf, your score is the sum of byte lengths of...

Roll cake phrases code-golf ascii-art string Roll cakes are delicious sweets made with a layer of sponge cake, a layer of cream (or icecream), rolled as a spiral, see Wikipedia. Your task is to get a phrase from standard input, strip the spaces out, and roll it as a roll cake starting from the...

Identify ALL the Interpreters! A previous question asked you to identify which of 3 languages a given script was written in. In this challenge, you will identify as many black-boxed interpreters/compilers as you can. Process Your code will consist of two parts: 1) A file to feed to the myst...

Reverse Factorial Your task is write a program or function which takes a positive integer, and returns/outputs its reverse factorial (i.e, given x, return n where n! = x). If it is not a factorial number, return a distinct value such as none, null or -1. Test Cases 1 -> 1 2 -> 2 24 ->...

Background Summer is well over, and a lot of us miss the sun, the beaches, the waves of the ocean... This challenge aims at cheering them up by reminding them of the sea. The challenge Here is the sea : ** ** ** ** ** ...

Don't you hate it when there's something wrong with brackets in your code? Don't know if our proposed solution is good in terms of user experience, but we won't know untill we try! I'll give you a string that consists only of 2 type of brackets: square ('[', ']') and round ('(', ')'). We want th...

Generate n-ary numbers A secondary number is a positive integer whose prime factors (without multiplicity) are all less than or equal to its square root. 4 is a secondary number, because its only prime factor is 2, which equals its square root. However, 15 is not a secondary number, because it h...