# Okarin99's solution

## to Prime Factors in the Rust Track

Published at Jul 12 2020 · 0 comments
Instructions
Test suite
Solution

Compute the prime factors of a given natural number.

A prime number is only evenly divisible by itself and 1.

Note that 1 is not a prime number.

## Example

What are the prime factors of 60?

• Our first divisor is 2. 2 goes into 60, leaving 30.
• 2 goes into 30, leaving 15.
• 2 doesn't go cleanly into 15. So let's move on to our next divisor, 3.
• 3 goes cleanly into 15, leaving 5.
• 3 does not go cleanly into 5. The next possible factor is 4.
• 4 does not go cleanly into 5. The next possible factor is 5.
• 5 does go cleanly into 5.
• We're left only with 1, so now, we're done.

Our successful divisors in that computation represent the list of prime factors of 60: 2, 2, 3, and 5.

You can check this yourself:

• 2 * 2 * 3 * 5
• = 4 * 15
• = 60
• Success!

## 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
``````

## 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

The Prime Factors Kata by Uncle Bob http://butunclebob.com/ArticleS.UncleBob.ThePrimeFactorsKata

## Submitting Incomplete Solutions

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

### prime-factors.rs

``````use prime_factors::factors;

#[test]
fn test_no_factors() {
assert_eq!(factors(1), vec![]);
}

#[test]
#[ignore]
fn test_prime_number() {
assert_eq!(factors(2), vec![2]);
}

#[test]
#[ignore]
fn test_square_of_a_prime() {
assert_eq!(factors(9), vec![3, 3]);
}

#[test]
#[ignore]
fn test_cube_of_a_prime() {
assert_eq!(factors(8), vec![2, 2, 2]);
}

#[test]
#[ignore]
fn test_product_of_primes_and_non_primes() {
assert_eq!(factors(12), vec![2, 2, 3]);
}

#[test]
#[ignore]
fn test_product_of_primes() {
assert_eq!(factors(901_255), vec![5, 17, 23, 461]);
}

#[test]
#[ignore]
fn test_factors_include_large_prime() {
assert_eq!(factors(93_819_012_551), vec![11, 9539, 894_119]);
}``````
``````struct PrimeNumberCounter {
count: u64,
prime_numbers: Vec<u64>,
}

count: 1,
prime_numbers: Vec::new(),
}
}
}

type Item = u64;

fn next(&mut self) -> Option<Self::Item> {
loop {
self.count += 1;
if self
.prime_numbers
.iter()
.all(|&prime| self.count % prime != 0)
{
self.prime_numbers.push(self.count);
return Some(self.count);
}
}
}
}

pub fn factors(n: u64) -> Vec<u64> {
let mut num = n;
let mut res = Vec::new();
while num % prime == 0 {
num /= prime;
res.push(prime);
}

if num == 1 {
return res;
}
}

unreachable!();
}``````