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# n0mn0m's solution

## to Leap in the Rust Track

Published at Nov 02 2020 · 0 comments
Instructions
Test suite
Solution

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.

## 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 may use the `arithmetic remainder` operator to test for divisibility.

## Rust Installation

Refer to the exercism help page for Rust installation and learning resources.

## Writing the Code

Execute the tests with:

``````\$ cargo test
``````

All but the first test have been ignored. After you get the first test to pass, open the tests source file which is located in the `tests` directory and remove the `#[ignore]` flag from the next test and get the tests to pass again. Each separate test is a function with `#[test]` flag above it. Continue, until you pass every test.

If you wish to run all ignored tests without editing the tests source file, use:

``````\$ cargo test -- --ignored
``````

To run a specific test, for example `some_test`, you can use:

``````\$ cargo test some_test
``````

If the specific test is ignored use:

``````\$ cargo test some_test -- --ignored
``````

To learn more about Rust tests refer to the online test documentation

Make sure to read the Modules chapter if you haven't already, it will help you with organizing your files.

## Further improvements

After you have solved the exercise, please consider using the additional utilities, described in the installation guide, to further refine your final solution.

To format your solution, inside the solution directory use

``````cargo fmt
``````

To see, if your solution contains some common ineffective use cases, inside the solution directory use

``````cargo clippy --all-targets
``````

## Submitting the solution

Generally you should submit all files in which you implemented your solution (`src/lib.rs` in most cases). If you are using any external crates, please consider submitting the `Cargo.toml` file. This will make the review process faster and clearer.

## Feedback, Issues, Pull Requests

The exercism/rust repository on GitHub is the home for all of the Rust exercises. If you have feedback about an exercise, or want to help implement new exercises, head over there and create an issue. Members of the rust track team are happy to help!

If you want to know more about Exercism, take a look at the contribution guide.

## 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.

### leap.rs

``````fn process_leapyear_case(year: u64, expected: bool) {
assert_eq!(leap::is_leap_year(year), expected);
}

#[test]
fn test_year_not_divisible_by_4_common_year() {
process_leapyear_case(2015, false);
}

#[test]
#[ignore]
fn test_year_divisible_by_2_not_divisible_by_4_in_common_year() {
process_leapyear_case(1970, false);
}

#[test]
#[ignore]
fn test_year_divisible_by_4_not_divisible_by_100_leap_year() {
process_leapyear_case(1996, true);
}

#[test]
#[ignore]
fn test_year_divisible_by_4_and_5_is_still_a_leap_year() {
process_leapyear_case(1960, true);
}

#[test]
#[ignore]
fn test_year_divisible_by_100_not_divisible_by_400_common_year() {
process_leapyear_case(2100, false);
}

#[test]
#[ignore]
fn test_year_divisible_by_100_but_not_by_3_is_still_not_a_leap_year() {
process_leapyear_case(1900, false);
}

#[test]
#[ignore]
fn test_year_divisible_by_400_leap_year() {
process_leapyear_case(2000, true);
}

#[test]
#[ignore]
fn test_year_divisible_by_400_but_not_by_125_is_still_a_leap_year() {
process_leapyear_case(2400, true);
}

#[test]
#[ignore]
fn test_year_divisible_by_200_not_divisible_by_400_common_year() {
process_leapyear_case(1800, false);
}

#[test]
#[ignore]
fn test_any_old_year() {
process_leapyear_case(1997, false);
}

#[test]
#[ignore]
fn test_early_years() {
process_leapyear_case(1, false);
process_leapyear_case(4, true);
process_leapyear_case(100, false);
process_leapyear_case(400, true);
process_leapyear_case(900, false);
}

#[test]
#[ignore]
fn test_century() {
process_leapyear_case(1700, false);
process_leapyear_case(1800, false);
process_leapyear_case(1900, false);
}

#[test]
#[ignore]
fn test_exceptional_centuries() {
process_leapyear_case(1600, true);
process_leapyear_case(2000, true);
process_leapyear_case(2400, true);
}

#[test]
#[ignore]
fn test_years_1600_to_1699() {
let incorrect_years = (1600..1700)
.filter(|&year| leap::is_leap_year(year) != (year % 4 == 0))
.collect::<Vec<_>>();

if !incorrect_years.is_empty() {
panic!("incorrect result for years: {:?}", incorrect_years);
}
}``````
``````pub fn is_leap_year(year: u64) -> bool {
match (year % 4, year % 100, year % 400) {
(0, 0, 0) => true,
(0, 0, _) => false,
(0, _, _) => true,
(_, _, _) => false,
}
}``````