Added code to find longest common subsequence

[freckles30]

Issue Id you have worked upon -

Kindly write your answer here

Briefly explain your program logic -

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Screenshots(Attach 2 screenshots of your own input and output) -

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Checklist:

Eg - If your code follow the below guidelines. Kindly change [] to [x]

All the conditions should be fulfilled for considering your code for merging -

• [] I have mentioned the question as comment in my solution file.
  

• [] My code follows the guidelines of this project.
  

• [] I have performed a self-review of my own code.
  

• [] I have commented my code.
  

• [] My code gives the correct output.
  

• [] I confirm that I have not copied the code from anywhere. In case its found that I have copied even after successful merge then I can be banned from the repository and hacktoberfest.
  

• [] I affirm that I strictly follow contributing guidelines and code of conduct.

[SarthakKeshari]

@freckles30,
Kindly create an issue first and then PR. And follow the PR template and contribution guidelines.
I am not closing this PR since this was your first time. You may refer CONTRIBUTING.md(present in the repository) and create an issue(iff program has not been done in repositories probable folders).

If above given lines follow, then kindly create an issue now and claim it. I will assign it to you.