# Questions tagged [counting]

For challenges regarding counting the number of occurrences of some characteristic.

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### Return all letter counts as an integer

Definition Given some string return an integer whose digits are the number ocurrences of a-z (case insensitive, in alphabetical order) in that string. Any character with 0 instances is skipped. ...
1k views

### Count count count

Description You have a list of integers and start counting from the first term to the next and continue from that to the next and so on.. How many times have you counted? For example given [ 2, 5, 3, ...
600 views

### Acyclic orientations of an n-dimensional cube

The goal of this challenge is to check and extend the OEIS sequence A334248: Number of distinct acyclic orientations of the edges of an n-dimensional cube. Take an n-dimensional cube (if n=1, this is ...
14k views

### Count up forever

Write a program that counts up forever, starting from one. Rules: Your program must log to STDOUT or an acceptable alternative, if ...
9k views

### Determine the depth of an array

A simple challenge for your Monday evening (well, or Tuesday morning in the other half of the world...) You're given as input a nested, potentially ragged array of positive integers: ...
2k views

### Find the "Recursive Size" of a List

Inspired by Find the “unwrapped size” of a list. Define the Recursive Size, RS, of a list containing no lists as its length (number of items contained) and the ...
526 views

### Counting and so on

Content You count numbers every day (I think), and most of you know how to count properly, the one next to 1 is 2, and the next ...
5k views

### Detriplicate a string

A lot of languages have built-in ways to get rid of duplicates, or "deduplicate" or "uniquify" a list or string. A less common task is to "detriplicate" a string. That is,...
2k views

### Finding the most 'unique' word

Using you language of choice, write the shortest function/script/program you can that will identify the word with the highest number of unique letters in a text. Unique letters should include any ...
5k views

### Cantor's unspeakable numbers

An unspeakable number is a number which is divisible by seven or has seven as one of its digits. A children game is to count skipping unspeakable numbers ...
405 views

### Remove duplicates from list and order it by count? (python 3)

How do I remove all duplicates from list and order it based on count? ...
215 views

### Black and white shirt 2

This is a more complicated version of this puzzle. The premise is the same but a few rules differ in a few key places, making for a more complex problem. Assume I have some number of black shirts and ...
1k views

### Possible periods of input

Background: Take this input as an example: 1 1 2 1 1 2 1 3 1 3 If you look only at the first few digits, between 1 1 2 and <...
2k views

### How many Sets are there?

This is similar in concept to this challenge, but that is pretty restrictive on input and output and I think opening up these restrictions would lead to a completely different set of solutions that ...
6k views

### A scene of Jimmy diversity

As you probably know, there have been multiple lovely Jimmy challenges recently popping up. In these challenges, you were challenged with our beloved friend's acrobatics skills. Now we've got a ...
1k views

### Number Lockers!

Given a positive integer < 100 (from 1 to 99, including 1 and 99), output that many lockers. A locker is defined as the following: ...
2k views

### Count forth and back then double up

Let's count... Count up to 2 and back to 1 Count up to 4 and back to 1 Count up to 6 and back to 1 ... ok you got it... put all these together and you'll get the following sequence ...
1k views

### Replace all items with their counts

Task: Given an array of numbers as input (you can choose what subset, such as integers or natural numbers), replace all items with the number of times they appear within the array. As an example, <...
534 views

### Roman Numeral Line Segments

Write a program or function that accepts an integer in the range 1..3999 as input and returns the number of line segments required to express that integer in standard Roman numerals (so you would use ...
11k views

### Count the number of ones in an unsigned 16-bit integer

Write some statement(s) which will count the number of ones in an unsigned sixteen-bit integer. For example, if the input is 1337, then the result is ...
4k views

On 4chan, a popular game is get. Every post on the site gets a sequential post ID. Since you can't influence or determine them, people try to guess (at least a part of) their own post number, usually ...
7k views

### Covering a Skyline with brush strokes

Given a non-negative integer skyline height list, answer how many uninterrupted 1-unit-high horizontal brush strokes are needed to cover it. [1,3,2,1,2,1,5,3,3,4,2]...
1k views

### Autogrammatic pairs

For today's task, we have two programs, P and Q, both in the same language. Each of them receives a single-character input. If P receives character K, P says how many times K appeared in Q. (You can ...
21k views

### Counting Grains of Rice

Consider these 10 images of various amounts of uncooked grains of white rice. THESE ARE ONLY THUMBNAILS. Click an image to view it at full size. A: B: C: D: E: F: G: H: I: J: Grain Counts: <...
2k 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. ...
4k views

### Count trailing truths

Inspired by, and in memory of, my dear friend and colleague, Dan Baronet, 1956 – 2016. R.I.P. He found the shortest possible APL solution to this task: Task Given a Boolean list, count the number of ...
898 views

### Count strictly overlapping substrings

Given two strings a and b, count how many times b occurs as a substring in ...
841 views

### Count the crossing words

Consider the following standard 15×15 crossword puzzle grid. We can represent this in ASCII art by using # for blocks and ...
924 views

### Analyze the flow

On a toroidal square grid (you can wrap around) where each cell indicates one direction (^ > ...
6k views

### Into how many pieces can you cut this string?

Consider a piece of string (as in "rope", not as in "a bunch of characters"), which is folded back and forth on the real line. We can describe the shape of the string with a list of points it passes ...
4k views

### Recursively count lines of code, excluding empty lines and comments

Requirement: Write a program (in any language) that counts the number of lines of code in files matching *.sh in the directory tree starting from the directory that ...
2k views

### Eye test - How many squares are in this picture?

The picture: Sick of the same old grid where the answer is simply a square pyramidal number? Accept the challenge and write a program that given a positive integer $n$ counts how many squares are ...
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### Molecules to Atoms

The Challenge Write a program that can break down an input chemical formula (see below), and output its respective atoms in the form element: atom-count. Input ...
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### Calculate the nth term of Golomb's self-describing sequence

Inspired by the previous question. Golomb's self-describing sequence g(n) is a sequence where any natural number n is repeated within the sequence g(n) times. The ...
916 views

### Count the unique fractions with only integers [closed]

Count the number of unique fractions with numerators and denominators from 1 to 100, and print the counted number. Example: 2/3 = 4/6 = ... Rules: You must actually count in some way. Only integers ...
3k views

### Non Unique Elements

Write a program which finds the non-unique elements of an array of signed integers. The resulting array can be in any order. Your answer may be a snippet which assumes the input to be stored in a ...
424 views

### Count cyclically self-describing lists

Cyclically self-describing lists A list $L$ of positive integers is cyclically self-describing, if the following conditions hold. $L$ is nonempty. The first and last elements of $L$ are ...
1k views

### Square-free semiprime counting

Definition A square-free semiprime is a natural number that is the product of two distinct prime numbers. The task Given a natural number n, count all square-free ...
2k views

### Prime Wednesdays

Prime Wednesdays Your task is to count the number of Wednesdays that fall on a prime day of the month in a particular year. For instance, 7-13-16 is a prime ...
6k views

### Count to 100 in Danish

Print all the numbers from 0-100 in the right order using the Danish way of counting How they count Like English, they have dedicated words for 0-20, 30, 40 and 100 Instead of saying ...
616 views

### Count from 1 to n in Negabinary and Negaquaternary

Instead of normal binary, you must count from 1 to an input in negabinary concatenated to negaquaternary. Here's an example, put in the form of an array: [11, 1102, 1113, 100130, 101131, 11010132, ...
662 views

### Saddle points in a matrix

A matrix can be thought of as the altitudes of a surface in 3D space. Consider the 8 neighbours (orthogonal and diagonal) of a cell as a cyclic sequence in clockwise (or anticlockwise) order. Some ...
462 views

### Number of solutions to a binary weight equation

We define $a(n)$ as the 1-indexed position of $n$ in the sequence of positive integers with the same binary weight, i.e. the same number of 1's in their binary representation. This is A263017. ...
3k views

### Alphabet Histogram

Given an input sentence consisting of one or more words [a-z]+ and zero or more spaces , output an ASCII-art histogram (bar ...
260 views

### count number of valid, unique sequences for moving on a 1xn board [closed]

There's a board with n squares in a horizontal row. You start in the leftmost square, and roll a 3-faced dice. 3 possible outcomes for a single roll of the die: Left: you move 1 step to the left, ...
3k views

### Find the occurrences of a character in an input string

Challenge Write a program that, given a string x which is 10 characters long and a character y, outputs the number of times ...
364 views

### Remove Duplicates From One List [duplicate]

Task: Remove all duplicates from one list of integers. A list is simply a sequence of connected values that allows the same values to be stored at different positions in this sequence. If an item ...
459 views

### How long is this string?

It's strange this question hasn't been asked yet, so here it is: Calculate the length of a string given through STDIN Rules As said, your string will be given through STDIN, not via command line ...