61 lines
1.7 KiB
Markdown
61 lines
1.7 KiB
Markdown
|
# Prime Factors
|
||
|
|
|
||
|
|
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!
|
||
|
|
|
||
|
|
* * * *
|
||
|
|
|
||
|
|
For installation and learning resources, refer to the
|
||
|
|
[exercism help page](http://exercism.io/languages/ruby).
|
||
|
|
|
||
|
|
For running the tests provided, you will need the Minitest gem. Open a
|
||
|
|
terminal window and run the following command to install minitest:
|
||
|
|
|
||
|
|
gem install minitest
|
||
|
|
|
||
|
|
If you would like color output, you can `require 'minitest/pride'` in
|
||
|
|
the test file, or note the alternative instruction, below, for running
|
||
|
|
the test file.
|
||
|
|
|
||
|
|
Run the tests from the exercise directory using the following command:
|
||
|
|
|
||
|
|
ruby prime_factors_test.rb
|
||
|
|
|
||
|
|
To include color from the command line:
|
||
|
|
|
||
|
|
ruby -r minitest/pride prime_factors_test.rb
|
||
|
|
|
||
|
|
|
||
|
|
## Source
|
||
|
|
|
||
|
|
The Prime Factors Kata by Uncle Bob [http://butunclebob.com/ArticleS.UncleBob.ThePrimeFactorsKata](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.
|