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# pfertyk's solution

## to Leap 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 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.

## Notes

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.

## Source

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.

### cases_test.go

``````package leap

// Source: exercism/problem-specifications
// Commit: e348053 leap: Apply new "input" policy
// Problem Specifications Version: 1.3.0

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

### leap_test.go

``````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++ {
IsLeapYear(y)
}
}
}``````
``````package leap

const testVersion = 3

func IsLeapYear(x int) bool {
return x % 4 == 0 && (x % 100 != 0 || x % 400 == 0)
}``````

### What can you learn from this solution?

A huge amount can be learned from reading other peopleâ€™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?