feat: add preOrder algorithm for tree data structure. test: add testc…

[Aryadev19]

…ases for preOrder algortihm

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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.
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• All new algorithms have a URL in their comments that points to Wikipedia or another similar explanation.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[appgurueu]

Implementation looks fine, apart from the fact that it has quadratic time complexity due to the constant array copying. Either fix this or add a big fat warning; I'd expect a pre-order traversal to have linear time complexity. Ideally you would use a generator instead of pushing to a list IMO.

The tests seem somewhat excessive for such a simple function (my rule of thumb roughly is 1:1 implementation to tests, 1:2 or 1:3 at most). You could also greatly shorten the tests by writing a utility constructor - something like const T = (left, value, right) => {left: left, value: value, right: right}.

I also think we should start consolidating (binary) tree algorithms in a (binary= tree class. A class would be a good idea to document the expected tree format and to group together related binary tree algorithms, including postorder and inorder traversal.

Finally, this is missing a doc comment; generally that would be fine for such a simple function ("self-documenting"), but I think that at least the tree format should be documented here.

[Aryadev19]

You are probably right, implementing all the methods in a tree class will be better. I am totally new to contributing to open source, so I am still learning about good test cases, I have one doubt one method is missing from the tree that is tree mirroring, I was thinking about doing that, so should it be a separate algorithm like in the python one or should I just update the tree file.

[appgurueu]

You should group algorithms working on the same tree structure in the same tree class. I assume you're going to implement a BinaryTree class?

[Aryadev19]

Yeah I think there's only a BST class, not binary tree, so I can implement binary tree and implement some of the methods, I'll work on that then!

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.