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exklamationmark's solution

to Space Age in the Go Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

Given an age in seconds, calculate how old someone would be on:

  • Earth: orbital period 365.25 Earth days, or 31557600 seconds
  • Mercury: orbital period 0.2408467 Earth years
  • Venus: orbital period 0.61519726 Earth years
  • Mars: orbital period 1.8808158 Earth years
  • Jupiter: orbital period 11.862615 Earth years
  • Saturn: orbital period 29.447498 Earth years
  • Uranus: orbital period 84.016846 Earth years
  • Neptune: orbital period 164.79132 Earth years

So if you were told someone were 1,000,000,000 seconds old, you should be able to say that they're 31.69 Earth-years old.

If you're wondering why Pluto didn't make the cut, go watch this youtube video.

No Stub

This may be the first Go track exercise you encounter without a stub: a pre-existing space_age.go file for your solution. You may not see stubs in the future and should begin to get comfortable with creating your own Go files for your solutions.

One way to figure out what the function signature(s) you would need is to look at the corresponding *_test.go file. It will show you what the package level functions(s) should be that the test will use to verify the solution.

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

Partially inspired by Chapter 1 in Chris Pine's online Learn to Program tutorial. http://pine.fm/LearnToProgram/?Chapter=01

Submitting Incomplete Solutions

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

cases_test.go

package space

// Source: exercism/problem-specifications
// Commit: 8d4df79 space-age: Apply new "input" policy
// Problem Specifications Version: 1.1.0

var testCases = []struct {
	description string
	planet      Planet
	seconds     float64
	expected    float64
}{
	{
		description: "age on Earth",
		planet:      "Earth",
		seconds:     1000000000,
		expected:    31.69,
	},
	{
		description: "age on Mercury",
		planet:      "Mercury",
		seconds:     2134835688,
		expected:    280.88,
	},
	{
		description: "age on Venus",
		planet:      "Venus",
		seconds:     189839836,
		expected:    9.78,
	},
	{
		description: "age on Mars",
		planet:      "Mars",
		seconds:     2329871239,
		expected:    39.25,
	},
	{
		description: "age on Jupiter",
		planet:      "Jupiter",
		seconds:     901876382,
		expected:    2.41,
	},
	{
		description: "age on Saturn",
		planet:      "Saturn",
		seconds:     3000000000,
		expected:    3.23,
	},
	{
		description: "age on Uranus",
		planet:      "Uranus",
		seconds:     3210123456,
		expected:    1.21,
	},
	{
		description: "age on Neptune",
		planet:      "Neptune",
		seconds:     8210123456,
		expected:    1.58,
	},
}

space_age_test.go

package space

import (
	"math"
	"testing"
)

func TestAge(t *testing.T) {
	const precision = 0.01
	for _, tc := range testCases {
		actual := Age(tc.seconds, tc.planet)
		if math.IsNaN(actual) || math.Abs(actual-tc.expected) > precision {
			t.Fatalf("FAIL: %s\nExpected: %#v\nActual: %#v", tc.description, tc.expected, actual)
		}
		t.Logf("PASS: %s", tc.description)
	}
}

func BenchmarkAge(b *testing.B) {
	for i := 0; i < b.N; i++ {
		for _, tc := range testCases {
			Age(tc.seconds, tc.planet)
		}
	}
}
package space

import (
	"math"
)

// Planet represents official planets in the Sol system.
type Planet string

const (
	Earth   Planet = "Earth"
	Mercury Planet = "Mercury"
	Venus   Planet = "Venus"
	Mars    Planet = "Mars"
	Jupiter Planet = "Jupiter"
	Saturn  Planet = "Saturn"
	Uranus  Planet = "Uranus"
	Neptune Planet = "Neptune"
)

// Age provides the age on a particular planet (in Earth years), given the age in seconds.
func Age(ageInSeconds float64, planet Planet) float64 {
	periodInEarthYear, exist := orbitalPeriodsInSecond[planet]
	if !exist {
		return math.NaN()
	}

	// NOTE: periodInEarthYear is assume to be > 0
	ageInEarthYear := ageInSeconds / periodInEarthYear
	return ageInEarthYear
}

const earthPeriodInSeconds = 31557600.0

var (
	orbitalPeriodsInSecond = map[Planet]float64{
		Earth:   1.0 * earthPeriodInSeconds,
		Mercury: 0.2408467 * earthPeriodInSeconds,
		Venus:   0.61519726 * earthPeriodInSeconds,
		Mars:    1.8808158 * earthPeriodInSeconds,
		Jupiter: 11.862615 * earthPeriodInSeconds,
		Saturn:  29.447498 * earthPeriodInSeconds,
		Uranus:  84.016846 * earthPeriodInSeconds,
		Neptune: 164.79132 * earthPeriodInSeconds,
	}
)

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