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lujanfernaud's solution

to Leap in the Go Track

Published at Sep 18 2019 · 0 comments
Test suite

Given a year, report if it is a leap year.

The tricky thing here is that a leap year in the Gregorian calendar occurs:

on every year that is evenly divisible by 4
  except every year that is evenly divisible by 100
    unless the year is also evenly divisible by 400

For example, 1997 is not a leap year, but 1996 is. 1900 is not a leap year, but 2000 is.

If your language provides a method in the standard library that does this look-up, pretend it doesn't exist and implement it yourself.


Though our exercise adopts some very simple rules, there is more to learn!

For a delightful, four minute explanation of the whole leap year phenomenon, go watch this youtube video.

You will see a cases_test.go file in this exercise. This holds the test cases used in the leap_test.go. You can mostly ignore this file.

However, if you are interested... we sometimes generate the test data from a cross language repository. In that repo exercises may have a .json file that contains common test data. Some of our local exercises have an intermediary program that takes the problem specification JSON and turns in into Go structs that are fed into the <exercise>_test.go file. The Go specific transformation of that data lives in the cases_test.go 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.


JavaRanch Cattle Drive, exercise 3 http://www.javaranch.com/leap.jsp

Submitting Incomplete Solutions

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


package leap

// Source: exercism/problem-specifications
// Commit: 18875ec Leap: Improve the specification so that code generation is more readable - … (#1468)
// Problem Specifications Version: 1.5.1

var testCases = []struct {
	year        int
	expected    bool
	description string
	{2015, false, "year not divisible by 4 in common year"},
	{1970, false, "year divisible by 2, not divisible by 4 in common year"},
	{1996, true, "year divisible by 4, not divisible by 100 in leap year"},
	{2100, false, "year divisible by 100, not divisible by 400 in common year"},
	{2000, true, "year divisible by 400 in leap year"},
	{1800, false, "year divisible by 200, not divisible by 400 in common year"},


package leap

import "testing"

func TestLeapYears(t *testing.T) {
	for _, test := range testCases {
		observed := IsLeapYear(test.year)
		if observed != test.expected {
			t.Fatalf("IsLeapYear(%d) = %t, want %t (%s)",
				test.year, observed, test.expected, test.description)

// Benchmark 400 year interval to get fair weighting of different years.
func Benchmark400(b *testing.B) {
	for i := 0; i < b.N; i++ {
		for y := 1600; y < 2000; y++ {
package leap

// IsLeapYear reports if a year is a leap year.
func IsLeapYear(year int) bool {
	if year%400 == 0 {
		return true

	if year%4 == 0 && !(year%100 == 0) {
		return true

	return false

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