Adding QuickSort Algorithm

[anirudh-kac]

Fixes #273

Brief description of what is fixed or changed

I implemented the quick sort algorithm . Added required _partition function and quick_sort function in pydatastructs.linear_data_structures.algorithms
I checked all export statements and init files to make sure it's working

Other comments

This is the non parallel version.
I'm also working on the parallel version , but I was facing some issues with that.
Since some code from this will be reused and this is working fine , I'm making a PR for this version first

[codecov]

Codecov Report

Merging #274 into master will decrease coverage by 0.192%.
The diff coverage is 85.294%.

@@              Coverage Diff              @@
##            master      #274       +/-   ##
=============================================
- Coverage   98.810%   98.617%   -0.193%     
=============================================
  Files           23        23               
  Lines         2353      2387       +34     
=============================================
+ Hits          2325      2354       +29     
- Misses          28        33        +5     

Impacted Files	Coverage Δ
pydatastructs/linear_data_structures/__init__.py	100.000% <ø> (ø)
pydatastructs/linear_data_structures/algorithms.py	96.527% <85.294%> (-3.473%)	⬇️
pydatastructs/trees/heaps.py	97.927% <0.000%> (ø)
pydatastructs/trees/m_ary_trees.py	91.176% <0.000%> (ø)
pydatastructs/trees/binary_trees.py	97.364% <0.000%> (ø)
pydatastructs/trees/space_partitioning_trees.py	97.656% <0.000%> (ø)
...datastructs/linear_data_structures/linked_lists.py	99.596% <0.000%> (ø)

[czgdp1807]

This is recursive. Please convert it into iterative logic.

[czgdp1807]

You can use the notion of stacks to do it.

[czgdp1807]

Are you participating through GSSoC, 2020?

[czgdp1807]

Since some code from this will be reused

Where can this code be used other than in quick sort algorithm? Serial version isn't needed, only parallel version is to be added. Do not close this PR, just update this with the parallel version of quick sort and remove the sequential version.

[anirudh-kac]

@czgdp1807 , I tried using Stack from miscellaneous_data_structures in my implementation of iterative quick sort , however I'm getting import error when importing Stack
cannot import name 'DynamicOneDimensionalArray' from 'pydatastructs.linear_data_structures'

[anirudh-kac]

Yes I'm participating through GSSOC as of now

[czgdp1807]

I tried using Stack from miscellaneous_data_structures

You can use python list as a stack. No problems.

[czgdp1807]

Suggested change

.. [2] https://www.geeksforgeeks.org/quick-sort

Please use, wikipedia/university lectures/research papers as references.

[anirudh-kac]

Sorry for the delay, couldn't work for some time.
I removed the recursive logic but how can this be made parallel now? We have a single stack that will be accessed ,won't that be an issue? Can you guide me a little

[czgdp1807]

Well, a stack is a list. So you can access any element from inside it. Launch threads for some of the top elements. It's just like a tree, all the leafs are processed parallely in the bottom layer, then the second last, and so on till we reach the top.

[czgdp1807]

I think you forgot to add tests for your patch. See, tests folder under linear_data_structures.

[czgdp1807]

@anirudh-kac Are you working on it? Please do not close the PR.

[anirudh-kac]

@czgdp1807 sorry for replying late. I was having some trouble with the parallel implementation and got busy with some college stuff later tbh.
Any resource that might be helpful for implementing the parallel version?

[czgdp1807]

See, https://en.wikipedia.org/wiki/Quicksort#Parallelization and a lot PDFs on the web.

[robotjellyzone]

Hi @anirudh-kac are you still working on it ! feel free to ask your queries here

[anirudh-kac]

@robotjellyzone I had some trouble implementing the iterative parallel version of quick sort. I went through some resources over the internet but couldn't really figure out how to implement it. I'm still trying but I won't mind if anyone else takes over the issue as I've taken a lot of time

[robotjellyzone]

@robotjellyzone I had some trouble implementing the iterative parallel version of quick sort. I went through some resources over the internet but couldn't really figure out how to implement it. I'm still trying but I won't mind if anyone else takes over the issue as I've taken a lot of time

@anirudh-kac have you checked this https://en.wikipedia.org/wiki/Quicksort#Parallelization already? if so then that's totally fine i would add upforgrabs for other contributors !

[Arvind-raj06]

Is this PR still in progress or should I take it over!

[sidhu1012]

Is this PR still in progress or should I take it over!

You can take it over.

[czgdp1807]

Closing in favor of #314