Published at May 19 2019
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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:

```
1 2 3
8 9 4
7 6 5
```

```
1 2 3 4
12 13 14 5
11 16 15 6
10 9 8 7
```

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.

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.

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

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

```
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 allows the creation of spiral matrices, for instance :
// 1 2 3 4
// 12 13 14 5
// 11 16 15 6
// 10 9 8 7
package spiralmatrix
import ()
// Function SpiralMatrix generates a spiral matrix of size n.
func SpiralMatrix(n int) [][]int {
var counter int = 1
var matrix = make([][]int, n)
for i := 0; i < n; i++ {
matrix[i] = make([]int, n)
}
for i := 0; i < (n+1)/2; i++ {
// From UP-LEFT to UP-RIGHT
for k := i; k < n-i; k++ {
matrix[i][k] = counter
counter++
}
// From UP-RIGHT to DOWN-RIGHT
for j := i + 1; j < n-i; j++ {
matrix[j][n-1-i] = counter
counter++
}
// From DOWN-RIGHT to DOWN-LEFT
for k := n - i - 2; k >= i; k-- {
matrix[n-1-i][k] = counter
counter++
}
// From DOWN-LEFT to UP-LEFT
for j := n - i - 2; j >= i+1; j-- {
matrix[j][i] = counter
counter++
}
}
return matrix
}
```

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

- What compromises have been made?
- Are there new concepts here that you could read more about to improve your understanding?

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