# Questions tagged [matrix]

A matrix is a list of numbers arranged in a rectangle with rows and columns. In programming, it is also known as a 2D array. Use this tag if your challenge is about manipulating matrices.

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### Zigzagify a Matrix

As part of its compression algorithm, the JPEG standard unrolls a matrix into a vector along antidiagonals of alternating direction: Your task is to take a matrix (not necessarily square) and return ...
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### Simplify matrix input!

I have written a few challenges related to matrices, and common for all are that I use a format like the one below when representing the matrices, both in examples and in test cases: ...
629 views

### Draw diagonal positions of me squared

Based on the interpretation user @ThePirateBay made from the first version of my own challenge Output diagonal positions of me squared now I challenge you to make ASCII art that draws diagonal lines ...
656 views

### Reconstruct a zigzagified matrix

As part of its compression algorithm, the JPEG standard unrolls a matrix into a vector along antidiagonals of alternating direction: Your task is to take the unrolled vector along with the matrix ...
3k views

### Determinant of an Integer Matrix

Given a square integer matrix as input, output the determinant of the matrix. Rules You may assume that all elements in the matrix, the determinant of the matrix, and the total number of elements in ...
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### Orthodiagonal steps

It's a common problem to navigate in a 2D matrix. We've seen it many times and will see again. So let's help future us and develop the shortest solutions to generate all eight possible steps in a 2D ...
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### Solve a 2x2 Eigensystem

For those with a little linear algebra background, the challenge is as simple as this: determine the eigenvalues and eigenvectors of a given complex 2x2 matrix. You may skip ahead to The Challenge for ...
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### Make it explode!

Take a matrix of positive integers as input, and make it explode! The way you explode a matrix is by simply adding zeros around every element, including the outside borders. Input/output formats are ...
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### Generalized matrix trace

Inspiration. Given (by any means): A two-argument (or single argument consisting of a two-element list) black box function, f: ℤ+ × ℤ+ → ℤ+ (input and output are ...
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### Diamondize a Matrix

Given a matrix, output a representation of the matrix where the top left element is on top, the anti-diagonal is the central row and the bottom right element is at the bottom. For example, consider ...
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### Cops: Make a regex - Make a snake

This is the cop's thread. The robber's thread is here. Write a code that takes an input n and creates a n-by-n "snake matrix". A snake matrix is a matrix that ...
5k views

### Construct the Identity Matrix

The challenge is very simple. Given an integer input n, output the n x n identity matrix. The identity matrix is one that has <...
799 views

### Jordan Decomposition

Important note: Because this challenge only applies to square matrices, any time I use the term "matrix", it is assumed that I am referring to a square matrix. I am leaving off the "square" ...
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### Ascending matrix

The "ascending matrix" is an infinite matrix of whole numbers (0 included) in which any element is the smallest available element which has not been previously used on the respective row and column: <...
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### Do Matrix Multiplication!

In mathematics, matrix multiplication or the matrix product is a binary operation that produces a matrix from two matrices. The definition is motivated by linear equations and linear transformations ...
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### Calculate the Kronecker Product

Related, but very different. In the examples below, A and B will be 2-by-2 matrices, and the matrices are one-indexed. A ...
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### Verify Eigenpairs

In this challenge, you will be given a square matrix A, a vector v, and a scalar λ. You will ...
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### Codegolf the permanent

The challenge is to write codegolf for the permanent of a matrix. The permanent of an n-by-n matrix ...
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### Output diagonal positions of me squared

Given a number n, Output an ordered list of 1-based indices falling on either of the diagonals of an n*n square matrix. ...
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### There, I fixed it (with rope)

Related: Rather similar (but much easier) challenge horizontally: There I fixed it (with tape) Challenge: Given a string only containing upper- and/or lowercase letters (whichever you prefer) and ...
560 views

### 2D Array Middle Point

Given dimensions of a 2D array, except 1xn, that results in an odd number of elements, find the midpoint index. Example: Input is 3x5, representing the 2D array [0,0] [0,1] [0,2] [0,3] [0,4] [...
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### Advent Challenge 7: Balance the storage carts!

<< Prev Next >> After some careful analysis, Santa was able to determine the dock size ranges and get the presents into the correct transportation dock. Now, he needs you to help him balance ...
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### The Hungry Mouse

Sixteen piles of cheese are put on a 4x4 square. They're labeled from $1$ to $16$. The smallest pile is $1$ and the biggest one is $16$. The Hungry Mouse is so hungry that it always goes ...
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### Is the matrix centrosymmetric… and so is the code?

Defintion A centrosymmetric matrix is a square matrix that is symmetric about its center. More rigorously, a matrix $A$ of size $n \times n$ is centrosymmetric if, for any \\$i,\: j \in ([1, n] \...
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### Fire propagation simulator

Suppose we have a matrix like this: 11111 12221 12321 12221 11111 This matrix represents a terrain, and each cell represents a portion of terrain. The number in ...
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### Friar simulator

The brethren from the order of St Golfus the Concise have a tradition of reciting a short prayer whenever they see someone make the sign of the cross. Due to the high level of sin measured among ...
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### Binary Numbers Magic Trick

The challenge is simply; output the following six 2D integer arrays: ...
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### Calculate the permanent as quickly as possible

The challenge is to write the fastest code possible for computing the permanent of a matrix. The permanent of an n-by-n matrix ...
3k views

### Symbolic matrix multiplication

There are lots of different ways to explain matrix multiplication. I'll stick with a single figure since I believe most people here are familiar with it (and the figure is very descriptive). If you ...
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### Check if all non-zero elements in a matrix are connected

Input: A matrix containing integers in the range [0 - 9]. Challenge: Determine if all non-zero elements are connected to each other vertically and/or horizontally. Output: A truthy value if all ...
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Definition An arrowhead matrix is a matrix that has all entries equal to 0, except the ones on the main diagonal, top row and leftmost column. In other words, the matrix should look like this: * * * ...
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### Rotating a 2D Matrix

Let's say I have the following (2D) matrix: [[1, 2, 3, 4 ], [5, 6, 7, 8 ], [9, 10, 11, 12], [13, 14, 15, 16]] Rotate the matrix counterclockwise ...
604 views

### Minimum rectangle cover

Rectangle covers Suppose you have a matrix of bits, for example the following. 1 1 0 0 0 1 1 0 1 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 1 0 1 1 1 1 0 1 1 0 1 1 1 0 1 ...
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### Square-Random-Symmetrical

Challenge Write a program or a function that returns or prints a square-random-symmetrical matrix. Input N: The size of the matrix i.e 6 x 6 Output The matrix. ...
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### Perfect Squares Without Borders

Given n=m^2, return a list of integers that do not border the m x m grid of integers from ...
519 views

### Unicode rectangles

Given a matrix a of characters from u=" ╶╺╵└┕╹┖┗╴─╼┘┴┶┚┸┺╸╾━┙┵┷┛┹┻╷┌┍│├┝╿┞┡┐┬┮┤┼┾┦╀╄┑┭┯┥┽┿┩╃╇╻┎┏╽┟┢┃┠┣┒┰┲┧╁╆┨╂╊┓┱┳┪╅╈┫╉╋" the ...
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### Matrix in “slash” order

Given two positive numbers N >= 2 and N <= 100 create a matrix which follows the following rules: First Number starts at ...
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### Overlapping String-Blocks

Challenge: Given a list of multi-line strings, overlap them (in the top-left) and output the result. Example: Input: ["aaaa\naaaa\naaaa\naaaa","bb\nbb\nbb","c"] ...
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### Matrix with 1 to L(n), in all n columns

Challenge: Take a list, L containing positive integers as input: 3 5 2 1 6 and create a matrix where the n'th column contains the vector 1:L(n), where shorter ...
603 views

### Is my kids' alphabet mat properly grouped by colors?

My kids have an alphabet mat to play with, something like this: After months with the tiles of the mat randomly placed, I got tired and placed all the tiles of the mat grouped by sections according ...
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### Trim that distracting background off!

Isn't it annoying when you're taking a picture, but the background detracts from the actual substance of the image? I'd say it is. I need to know how much I should crop so that I get rid of this ...
590 views

### Minimal taxicab distance map

Challenge description In taxicab metric, a distance between two points is defined as: Consider a matrix with only zeros and ones: ...
485 views

### Count the contiguous submatrices

Migrated from chat Given two non-empty non-negative integer matrices A and B, answer the number of times A occurs as a contiguous, possibly overlapping, submatrix in B. Examples/Rules 0. There may ...
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### Robbers: Crack the regex - Make a snake

This is the robber's thread. The cop's thread is here. A snake matrix is a square matrix that follows this pattern: 3-by-3: 1 2 3 6 5 4 7 8 9 and 4-by-4: ...
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### Find the Cell's Neighbours

...or Toroidal Moore Neighbourhoods Given positive integers h, w and a non-negative integer ...
990 views

### Are there N consecutive occurrences of a number in a row/column in a matrix?

Take a matrix A consisting positive integers, and a single positive integer N as input, and determine if there are at least N consecutive occurrences of the same number in any row or column in the ...
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### Sum the diagonals

Take a matrix of positive integers as input, and output the individual sums of the elements on the diagonal lines through the matrix. You shall only count the lines that goes diagonally down and to ...