Sliding window problem

[seema-Patel888]

Hi, I would like to contribute a sliding window problem to the folder. Please merge it.

[harshita9621]

Can you please assign me this . I am part of hacktoberfest2021.

[Saicharan67]

Add problems in sliding window topic @seema-Patel888

[singhshrey27]

Hi, I would like to contribute for sliding window problem. Can you please assign this task to me?

[singhshrey27]

I have made a pull request , please merge the code