## Top new questions this week:

### R.E.P.A.I.R. T.H.E. K.E.Y.B.O.A.R.D

Sequel of this AWESOME challenge You, a genius tech prodigy detective, have successfully disarmed the bomb and want to break into the computer. The police found the password ...

string code-challenge restricted-source

### Output a Latin Square

An \$n\times n\$ Latin Square is a grid containing exactly \$n\$ distinct values where the values in each row and column are distinct. For example, \begin{matrix} A & B & C \\ C & A &...

code-golf array-manipulation matrix

### How many bystanders will help?

Flavortext The Bystander Effect is a phenomenon where individuals are less likely to help a victim if other people are present. The idea is that as there are more people around, the individual burden ...

code-golf math array-manipulation

### Calculate Home Primes

The Home Prime of an integer \$n\$ is the value obtained by repeatedly factoring and concatenating \$n\$'s prime factors (in ascending order, including repeats) until reaching a fixed point (a prime). ...

code-golf math number-theory primes

### Make it prime with the smallest suffix

Given a positive integer as input, output the smallest positive integer such that appending its digits (in base 10) to the end of the input number will form a prime number. Examples ...

code-golf primes

### Close neighbours stick together

Given a list of positive digits, return that list with consecutive elements grouped together. For example: ...

code-golf array-manipulation

### The half-step of Fibonacci

Challenge Implement the 1-indexed sequence A054049, which starts like this: ...

code-golf math sequence fibonacci

## Greatest hits from previous weeks:

### How can I use cmp(a,b) with Python3?

I was told that using the cmp function can be very useful in code-golf. But unfortunately, Python 3 doesn't have a cmp function. ...

code-golf tips python

### Implement the Thanos sorting algorithm

The sorting algorithm goes like this: While the list is not sorted, snap half of all items (remove them from the list). Continue until the list is sorted or only one item remains (which is sorted by ...

code-golf sorting

### Polygon prefixes

Polygons are named after the number of sides that they have. A pentagon has 5 sides, an octagon has 8 sides. But how are they named? What's the name for a 248-sided polygon? All polygons are suffixed ...

code-golf geometry

### Print every character your program doesn't have

Your task is to build a program (using only printable ASCII characters and/or tabs and newlines) that prints out exactly the characters in the printable ASCII space (...

code-golf self-referential

### American Gothic in the palette of Mona Lisa: Rearrange the pixels

You are given two true color images, the Source and the Palette. They do not necessarily have the same dimensions but it is guaranteed that their areas are the same, i.e. they have the same number of ...

popularity-contest graphical-output image-processing color

### Hard code golf: Regex for divisibility by 7

Matthias Goergens has a 25,604-character (down from the original 63,993-character) regex to match numbers divisible by 7, but that includes a lot of fluff: redundant parentheses, distribution (...

code-golf math regular-expression

### "Hello, World!"

So... uh... this is a bit embarrassing. But we don't have a plain "Hello, World!" challenge yet (despite having 35 variants tagged with hello-world, and counting). While this is not the most ...

code-golf string kolmogorov-complexity hello-world

## Can you answer this question?

### Golfing Expressions

We can write mathematical expressions using the standard math operators (,),+,...

string parsing polynomials test-battery expression-building