# mstranger's solution

## to Spiral Matrix in the Go Track

Published at Jul 25 2019 · 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
``````

## Running the tests

To run the tests run the command `go test` from within the exercise directory.

If the test suite contains benchmarks, you can run these with the `--bench` and `--benchmem` flags:

``````go test -v --bench . --benchmem
``````

Keep in mind that each reviewer will run benchmarks on a different machine, with different specs, so the results from these benchmark tests may vary.

## Further information

For more detailed information about the Go track, including how to get help if you're having trouble, please visit the exercism.io Go language page.

## Source

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

## Submitting Incomplete Solutions

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

### spiral_matrix_test.go

``````package spiralmatrix

import (
"reflect"
"testing"
)

var testCases = []struct {
description string
input       int
expected    [][]int
}{
{
description: "empty spiral",
input:       0,
expected:    [][]int{},
},
{
description: "trivial spiral",
input:       1,
expected: [][]int{
{1},
},
},
{
description: "spiral of size 2",
input:       2,
expected: [][]int{
{1, 2},
{4, 3},
},
},
{
description: "spiral of size 3",
input:       3,
expected: [][]int{
{1, 2, 3},
{8, 9, 4},
{7, 6, 5},
},
},
{
description: "spiral of size 4",
input:       4,
expected: [][]int{
{1, 2, 3, 4},
{12, 13, 14, 5},
{11, 16, 15, 6},
{10, 9, 8, 7},
},
},
}

func TestSpiralMatrix(t *testing.T) {
for _, testCase := range testCases {
matrix := SpiralMatrix(testCase.input)
if !reflect.DeepEqual(matrix, testCase.expected) {
t.Fatalf("FAIL: %s\n\tSpiralMatrix(%v)\nexpected: %v\ngot     : %v",
testCase.description, testCase.input, testCase.expected, matrix)
}
t.Logf("PASS: %s", testCase.description)
}
}

func BenchmarkSpiralMatrix(b *testing.B) {
for i := 0; i < b.N; i++ {
for _, testCase := range testCases {
SpiralMatrix(testCase.input)
}
}
}``````
``````package spiralmatrix

// SpiralMatrix builds a square matrix (n x n) of numbers in spiral order.
func SpiralMatrix(n int) [][]int {
res := make([][]int, n)
for i := range res {
res[i] = make([]int, n)
}

fillSpiral(res, 1)

return res
}

// fillSpiral fills the given matrix with numbers
func fillSpiral(m [][]int, s int) int {
current := s
n := len(m)

for t := n; t > n/2; t-- {
for j := n - t; j < t; j++ {
m[n-t][j] = current
current++
}

for i := n - t + 1; i < t; i++ {
m[i][t-1] = current
current++
}

for j := t - 2; j > n-t; j-- {
m[t-1][j] = current
current++
}

for i := t - 1; i > n-t; i-- {
m[i][n-t] = current
current++
}
}

return current
}``````