The focus here is on the data structures and solution, not system design. Let me know if you need more clarification.

The problem is to implement two reddit features, being able to upvote/downvote a post and being able to get x top posts. For the "post" structure it can be as simple as an id and number of votes.

something like this:

class Post  {
	int id;
	int upvotes;
}

class Reddit {
	public void upvoteDownvote(int postID) {
	}
 
	public List<Integer> getTopKPosts(int k) {
	}
}

Im not sure how to solve this problem, first thing that comes to mind is to use a heap to keep track of most upvoted posts but if you upvote/downvote that post you need to update the heap and somehow find that one post, you could make a helper map or something to keep track of that instance of the post class with an id. The second thing that comes to mind is perhaps a linked list that we manually sort, after the inital setup of application, since a upvote/downvote is only adding or subtracting 1 to the value we can compare the node to its neighbors and move it accordingly.

Let me know what you guys think.

Thanks!