# Questions tagged [matrix]

This tag is for challenges involving matrices. A matrix, also known as a 2D array, is a list of numbers arranged in a rectangle with rows and columns.

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### Transposes and Diagonals

For this challenge, you should write a program or function which outputs the diagonals of a given square matrix. However, if you transpose the rows and columns of your solution's source code, it ...
1k views

### 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: ...
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### 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 ...
2k views

### Index of the row with most non-zero elements

This is a simple one: Take a matrix of integers as input, and output the index of the row with the most non-zero elements. You may assume that there will only be one row with the most non-zero ...
2k views

### 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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### 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 ...
584 views

### Interlaced Rotations

Challenge Given a square matrix of characters (single-byte printable ASCII characters), rotate each "ring" of the matrix in opposite directions. Let's take an example: ...
895 views

### Game of Life and Fatigue

Stewie's Game of Life and Fatigue is quite similar to the more famous Conway's Game of Life. The universe of the Stewie's Game of Life and Fatigue (GoLF) is an infinite two-dimensional orthogonal ...
3k views

### Create a checkerboard matrix

Take a positive integer n as input, and output a n-by-n checkerboard matrix consisting of 1 and 0. The top left digit should always be 1. Test cases: ...
637 views

### Fix my notation for lists of matrices, part 1

Sometimes, I have lists of constant matrices in my code: [ [[1, 0], [0, 1]], [[1, 0], [0,-1]], [[0, 1], [1, 0]], [[0,-1], [1, 0]] ] That's ...
4k views

### Sum of first row and column, then second row and column ... and so on

Take a non-empty matrix / numeric array containing positive integers as input. Return, in this order, the sums of the first row and column, then the second row and column and continue until there aren'...
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### Check if a matrix is a Toeplitz matrix

You will be given a two-dimensional array and a number and you are asked to find whether the given matrix is Toeplitz or not. A matrix is a Toeplitz matrix if every descending diagonal, going from ... 2k views

### 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 ...
611 views

### Is magic possible?

A magic square is an n-by-n square grid, filled with distinct positive integers in the range 1,2,...n^2, such that each cell contains a different integer and the sum of the integers in each row, ...
2k views

### Verify Eigenpairs

In this challenge, you will be given a square matrix A, a vector v, and a scalar λ. You will ...
590 views

### Lists and arrays, part by part

In this challenge, you'll get four different but somewhat related tasks that must be solved in a specific manner. First, I'll explain the tasks, then follows an explanation of how you must solve it. ...
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Rules No cell range references (A2:B3). Maximum 9 rows and 9 columns. No circular references or formula errors. Empty cells evaluate to ...
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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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### 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 ...
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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 ...
588 views

### Find the submatrix with the smallest mean, 2.0

You're given a n-by-m matrix of integers, where n,m > 3. Your task is to find the 3-by-3 sub-matrix that has the lowest mean, and output this value. Rules and clarifications: The integers will be ...
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### Find the submatrix with the smallest mean

You're given a n-by-m matrix of integers, where n,m > 3. Your task is to find the 3-by-3 sub-matrix that has the lowest mean, and output this value. Rules and clarifications: The integers will be ...
4k 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 ...
806 views

### Construct a Gaussian Matrix

Gaussian blur is a method used for blurring images smoothly. It involves creating a matrix which will be used by convolving it with the pixels of an image. In this challenge, your task is to construct ...
697 views

### Find the rows which make each column have one True (was: Knuth's Algorithm X)

Task Given a Boolean matrix, find one (or optionally more) subset(s) of rows which have exactly one True in each column. You may use any algorithm, but must support very large matrices, like the last ... 