Added isCompositeNumber.js

[tehliang]

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Describe your change:

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new JavaScript files are placed inside an existing directory.
• All filenames should use the UpperCamelCase (PascalCase) style. There should be no spaces in filenames.
  Example:UserProfile.js is allowed but userprofile.js,Userprofile.js,user-Profile.js,userProfile.js are not
• All new algorithms have a URL in its comments that points to Wikipedia or other similar explanation.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[appgurueu]

Isn't this the same as the already implemented check for "perfect numbers"?

NVM, should've read carefully.

[tehliang]

Isn't this the same as the already implemented check for "perfect numbers"?

No, they are not the same.
From Wikipedia and the internet.
A perfect number is a positive integer equal to the sum of its positive divisors, excluding the number itself.
For instance, 6 has divisors 1, 2 and 3 (excluding itself), and 1 + 2 + 3 = 6, so 6 is a perfect number.

A composite number is a positive integer that can be formed by multiplying two smaller positive integers. Equivalently, it is a positive integer that has at least one divisor other than 1 and itself.
For example, the integer 14 is a composite number because it is the product of the two smaller integers 2 × 7.

Example:
35 is a composite number but not a perfect number because
1 + 5 + 7 not equal to 35
while 35 has more than two factors, i.e. 1, 5, 7, 35.
Which makes 35 a composite number because 35 has more than two factors.

[appgurueu]

Looks good to me. You could perhaps deduplicate the factorization code (if the current APIs aren't too clunky to use).

[raklaptudirm]

In my opinion, this is largely a duplication of the PrimeCheck function. Using the fact that all prime numbers other than 2 and 3 are in the form 6n ± 1 is definitely an improvement, but it can be made on the PrimeCheck function itself. @appgurueu?

[appgurueu]

In my opinion, this is largely a duplication of the PrimeCheck function. Using the fact that all prime numbers other than 2 and 3 are in the form 6n ± 1 is definitely an improvement, but it can be made on the PrimeCheck function itself. @appgurueu?

Yes. isCompositeNumber(n) should just be !PrimeCheck(n) (with the exception of 1).

[raklaptudirm]

I think instead of duplicating the logic the 6n ± 1 improvement should be made on the PrimeCheck function itself.

[tehliang]

So any suggestions on how can I improve the algorithm?

[raklaptudirm]

You should remove the isComposite function and instead make your changes to the PrimeCheck function.

[tehliang]

You should remove the isComposite function and instead make your changes to the PrimeCheck function.

What changes should I make? I am a bit clueless... I am just proposing an algorithm to check composite numbers.

[appgurueu]

You should remove the isComposite function and instead make your changes to the PrimeCheck function.

What changes should I make? I am a bit clueless... I am just proposing an algorithm to check composite numbers.

Yes, but composite numbers are numbers that aren't prime, with the exception of one. You're thus duplicating primality sieve logic here. You should instead implement isComposite using PrimeCheck - or get rid of isComposite altogether - and improve the PrimeCheck function.

[tehliang]

You should remove the isComposite function and instead make your changes to the PrimeCheck function.

What changes should I make? I am a bit clueless... I am just proposing an algorithm to check composite numbers.

Yes, but composite numbers are numbers that aren't prime, with the exception of one. You're thus duplicating primality sieve logic here. You should instead implement isComposite using PrimeCheck - or get rid of isComposite altogether - and improve the PrimeCheck function.

Hmm, I still do not quite understand. PrimeCheck checks the prime number while the IsComposite checks the composite number. Yes, what the algo doing was reverse of each other, but the code is not the same. How can I implement PrimeCheck to check whether the number is composite using the PrimeCheck algorithm?

[appgurueu]

Hmm, I still do not quite understand. PrimeCheck checks the prime number while the IsComposite checks the composite number. Yes, what the algo doing was reverse of each other, but the code is not the same. How can I implement PrimeCheck to check whether the number is composite using the PrimeCheck algorithm?

function isComposite(number) {
  return number > 1 && !PrimeCheck(number)
}

there you go.

[stale]

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