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to Spiral Matrix in the Go Track

Published at Oct 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

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

var offsets = map[string][2]int{
	"right": [2]int{0, 1},
	"left":  [2]int{0, -1},
	"up":    [2]int{-1, 0},
	"down":  [2]int{1, 0},
}

var turnRight = map[string]string{
	"right": "down",
	"down":  "left",
	"left":  "up",
	"up":    "right",
}

// SpiralMatrix returns a matrix with integers that spiral clockwise
func SpiralMatrix(n int) [][]int {
	matrix := make([][]int, n)

	for i := range matrix {
		matrix[i] = make([]int, n)
	}

	return generateValues(0, 0, "right", matrix)
}

func generateValues(x, y int, direction string, matrix [][]int) [][]int {
	n := len(matrix)
	for val := 1; val <= n*n; val++ {
		matrix[x][y] = val
		x, y, direction = nextPosition(x, y, matrix, direction)
	}
	return matrix
}

func nextPosition(x int, y int, matrix [][]int, direction string) (nextX,
	nextY int,
	nextDirection string) {
	checkX := x + offsets[direction][0]
	checkY := y + offsets[direction][1]
	n := len(matrix)
	if checkOutOfBounds(checkX, checkY, n) || checkHasValue(checkX, checkY, matrix) {
		nextDirection = turnRight[direction]
	} else {
		nextDirection = direction
	}

	nextX = x + offsets[nextDirection][0]
	nextY = y + offsets[nextDirection][1]

	return
}

func checkOutOfBounds(x, y, n int) bool {
	return x < 0 || x >= n || y < 0 || y >= n
}

func checkHasValue(x, y int, matrix [][]int) bool {
	return matrix[x][y] != 0
}

Community comments

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oorion's Reflection

Curious if this is a decent implementation