Compression: Huffman Coding

[aladin002dz]

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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
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• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[appgurueu]

The other main point is string handling, which pretty consistently uses repeated concatenation here (e.g. for building prefixes (that one is mostly a non-concern though, since even with slow string concat, it'll be linearithmic time), for encoding / decoding). At least the encoding could be rewritten to use an array without making it any less readable.

Arguably all of this is fine in practice, as JS engines optimize string concatenation. I think it needs some comments alluding to this, though (I'm thinking something along the lines of "the string concatenation in a loop here is fine despite strings being immutable, as modern JS engines optimize it to be amortized constant time by delaying it (using ropes) and similar techniques").

I'm sorry about the unrelated changes due to formatting, that's due to a mistake on our part (see #1515).

Keep up the good work!

[appgurueu]

Why do you sort in every iteration?

[aladin002dz]

because when pushing a new node, the order may change.

[appgurueu]

Wouldn't it be more appropriate to use a max heap here (our existing implementations should work, you just need to import and use them), given that you always extract the most frequent ones and only push new ones?

[aladin002dz]

I think it would add a lot more complexity, wouldn't it?

[appgurueu]

I think the API of our heap should be pretty straightforward to use. A heap is pretty much the data structure for this use case; it would significantly help the time complexity. If you want me to, I can make the necessary changes.

[aladin002dz]

I'll try to implement it myself, then I'll need your valuable feedback and guidance.

[appgurueu]

Why have you duplicated the code? I think there should only be a heap-based implementation; it is strictly better (more efficient) than the array-based one and of similar code complexity.

[aladin002dz]

Why have you duplicated the code? I think there should only be a heap-based implementation; it is strictly better (more efficient) than the array-based one and of similar code complexity.
In progress to remove duplicates.

[appgurueu]

Adding the hacktoberfest-accepted label since we're close to the end of October, and this PR is pretty close to being accepted and merged later on.