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rootulp's solution

to Space Age in the Go Track

Published at Jun 01 2020 · 0 comments
Instructions
Test suite
Solution

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

  • Mercury: orbital period 0.2408467 Earth years
  • Venus: orbital period 0.61519726 Earth years
  • Earth: orbital period 1.0 Earth years, 365.25 Earth days, or 31557600 seconds
  • 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.

Simple Stub

The space_age.go "stub file" contains only one line with the correct package name and nothing more. This will be the usual pattern for future exercises. You will need to figure out the function signature(s).

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

Planet Type

The test cases make use of a custom Planet type that is sent to your function. You will need to implement this custom type yourself. Implementing this new custom type as a string should suffice.

Coding the solution

Look for a stub file having the name space_age.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

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: 28b3dac0 space-age: restrict seconds to fit within 32-bit int range
// Problem Specifications Version: 1.2.0

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:     2129871239,
		expected:    35.88,
	},
	{
		description: "age on Jupiter",
		planet:      "Jupiter",
		seconds:     901876382,
		expected:    2.41,
	},
	{
		description: "age on Saturn",
		planet:      "Saturn",
		seconds:     2000000000,
		expected:    2.15,
	},
	{
		description: "age on Uranus",
		planet:      "Uranus",
		seconds:     1210123456,
		expected:    0.46,
	},
	{
		description: "age on Neptune",
		planet:      "Neptune",
		seconds:     1821023456,
		expected:    0.35,
	},
}

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

// Planet names
type Planet string

const secondsInEarthYear = 31557600

var orbitalPeriods = map[Planet]float64{
	"Mercury": 0.2408467,
	"Venus":   0.61519726,
	"Earth":   1,
	"Mars":    1.8808158,
	"Jupiter": 11.862615,
	"Saturn":  29.447498,
	"Uranus":  84.016846,
	"Neptune": 164.79132,
}

// Age returns the age in years of someone on planet given their age in seconds.
func Age(ageInSeconds float64, planet Planet) float64 {
	return ageOnEarth(ageInSeconds) / orbitalPeriods[planet]
}

// AgeOnEarth returns the age of somone on Earth given their age in seconds.
func ageOnEarth(ageInSeconds float64) float64 {
	return ageInSeconds / secondsInEarthYear
}

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