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## to Spiral Matrix in the Julia Track

Published at Feb 13 2021 · 0 comments
Instructions
Test suite
Solution

Given the size, return a square matrix of numbers in spiral order.

The matrix should be filled with natural numbers, starting from 1 in the top-left corner, increasing in an inward, clockwise spiral order, like these examples:

###### Spiral matrix of size 3
``````1 2 3
8 9 4
7 6 5
``````
###### Spiral matrix of size 4
`````` 1  2  3 4
12 13 14 5
11 16 15 6
10  9  8 7
``````

## Source

Reddit r/dailyprogrammer challenge #320 [Easy] Spiral Ascension. https://www.reddit.com/r/dailyprogrammer/comments/6i60lr/20170619_challenge_320_easy_spiral_ascension/

## Version compatibility

This exercise has been tested on Julia versions >=1.0.

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### runtests.jl

``````using Test

include("spiral-matrix.jl")

@testset "Different valid values" begin
@testset "Empty spiral" begin
@test spiral_matrix(0) == Matrix{Int}(undef,0,0)
end
@testset "Trivial spiral" begin
@test spiral_matrix(1) == reshape(,(1,1))
end
@testset "Spiral of size 2" begin
@test spiral_matrix(2) == [1 2; 4 3]
end
@testset "Spiral of size 3" begin
@test spiral_matrix(3) == [1 2 3; 8 9 4; 7 6 5]
end
@testset "Spiral of size 4" begin
@test spiral_matrix(4) == [1 2 3 4; 12 13 14 5; 11 16 15 6; 10 9 8 7]
end
@testset "Spiral of size 5" begin
@test spiral_matrix(5) == [1 2 3 4 5; 16 17 18 19 6; 15 24 25 20 7; 14 23 22 21 8; 13 12 11 10 9]
end
end``````
``````function spiral(n::Int)
n == 0 && return Matrix{Int}(undef,0,0)

lin_map = []
ens = sort(cat([(4*k - 3, n - (k-1)) for k ∈ 1:n], [(4*k - 2, n - (k-1)) for k ∈ 1:n], dims=(1, 1)))
nums = sort(cat([(4*k - 1, k) for k ∈ 1:n], [(4*k, k+1) for k ∈ 1:n], dims=(1, 1)))

i = j = 1

for e ∈ sort(cat(ens, nums, dims=(1, 1)))[1:2*n - 1]
if e ∈ ens
if e % 2 == 1
while j != e
push!(lin_map, (i, j))
j += 1
end
elseif e % 2 == 0
while i != e
push!(lin_map, (i, j))
i += 1
end
end

elseif e ∈ nums
if e % 2 == 1
while j != e
push!(lin_map, (i, j))
j -= 1
end
elseif e % 2 == 0
while i != e
push!(lin_map, (i, j))
i -= 1
end
end
end
end

push!(lin_map, (i, j))

spiral_mat = zeros(Int64, n, n)

for k ∈ 1:length(lin_map)
spiral_mat[lin_map[k], lin_map[k]] = k
end

return spiral_mat
end``````

## Community comments

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### leadersheir's Reflection

Had lots of fun figuring this one out completely on my own for 3 days