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to Spiral Matrix in the Go Track

Published at Mar 17 2020 · 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

Coding the solution

Look for a stub file having the name spiral_matrix.go and place your solution code in that file.

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 implements a square matrix of numbers in spiral order.
package spiralmatrix

// SpiralMatrix returns matrix.
func SpiralMatrix(in int) [][]int {
	if in <= 0 {
		return [][]int{}
	}

	if in == 1 {
		return [][]int{{1}}
	}

	result := make([][]int, in)
	for i := 0; i < in; i++ {
		result[i] = make([]int, in)
	}

	count := 1
	for index := 0; index < in; index++ {

		for i := index; i < in-index; i++ {
			result[index][i] = count
			count++
		}

		for j := index + 1; j < in-index; j++ {
			result[j][in-1-index] = count
			count++
		}

		for i := in - 2 - index; i >= index; i-- {
			result[in-index-1][i] = count
			count++
		}

		for j := in - 2 - index; j > index; j-- {
			result[j][index] = count
			count++
		}
	}

	return result
}

//package spiralmatrix
//
//// SpiralMatrix returns a spiral matrix of size n
//func SpiralMatrix(n int) [][]int {
//	m := make([][]int, n)
//	for y := 0; y < n; y++ {
//		m[y] = make([]int, n)
//	}
//
//	x, y := 0, 0
//	dx, dy := 1, 0
//	for count := 1; count <= n*n; count++ {
//		m[y][x] = count
//		xx, yy := x+dx, y+dy
//		if xx < 0 || xx >= n || yy < 0 || yy >= n || m[yy][xx] != 0 {
//			dx, dy = -dy, dx
//		}
//		x, y = x+dx, y+dy
//	}
//
//	return m
//}

What can you learn from this solution?

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?