System design for a social network

I'm building a social network Imagine Twitter where people can follow and see posts.

I want to use to create an MVP. I only know Python and JavaScript, hence the backend in Python, the frontend in React.

I will have the following layers:

Authentication

My plan is to create and save users in Fire base. Seems to be a simple integration. It also seems relatively easy to migrate to a custom system as we grow.

Backend API

How does it work? bottle Sound? I can use it to create Firebase authentication token endpoints for all CRUD. I'm also thinking of using Django. It can do many things right away. The problem with Flask is a lot of work for validation / database models.

Database

I guess it has to be relational to see follower posts, participate in discussions, etc. So my vote is Postgres. I have to create users Table? I'm pretty sure that given the authenticated request, all user information will be passed and I can create all the necessary joins.

So my questions.

  1. Should I write my own Auth bottle / Django and create a user table myself?
  2. Should I use relational DB like Postgres?
  3. Responding is not very good for static URLs. For example, when a new person logs in, I want to create a static page with their profile, e.g. mysite.com/profile/{{username}}. Should I use next.js to pre-render the static content? For SEO etc. visibility. Does a reaction make sense?

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Java – System generated social network

On a given social network, the system automatically assigns friends to users, and users cannot add friends of their choice themselves. There are currently N users on the social network, labeled 2 to N + 1.

For every i-th user (where i is between 2 and N + 1), the system has assigned all users who are marked with a multiple of i as friends of the user (if possible).

One day, all users of the social network come together for a meeting and form groups so that every person in a group is a direct friend or a friend of a friend of every other person in this group.

Find the total number of groups.

Input specifications:

Input1: N, which indicates the number of users in the social network

Output specification:
Their function should return the number of groups that can be formed under certain conditions

Example 1:

Input1: 5
Edition: 2nd

Explanation:
Two groups are formed

2,3,4,6
5

Example 2:

Entry1: 10
Edition: 3

Explanation:
Three groups are formed:

2,3,4,5,6,8,9,10
7
11

Proposed solutions

Please optimize my solution. My solution works perfectly, but it doesn't look optimal.

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map.Entry;
import java.util.Set;

public class SocialNetwork {

    public static void main(String() args) {
        InputStreamReader r = new InputStreamReader(System.in);
        BufferedReader br = new BufferedReader(r);
        int value = 0;

        try {
            value = Integer.parseInt(br.readLine());
        } catch (IOException e) {
            System.out.println(e.getMessage());
        }

        HashMap> map = new HashMap<>();

        for (int i = 2; i <= value + 1; i++) {

            List list = new ArrayList<>();

            for (int j = 1; j * i <= value + 1; j++) {
                int tempValue = j * i;

                list.add(tempValue);

                if (i != tempValue) {
                    List addedList = map.get(tempValue);

                    if (addedList == null) {
                        addedList = new ArrayList<>();
                    }

                    if (!addedList.contains(i)) {
                        addedList.add(i);
                        map.put(tempValue, addedList);
                    }
                }
            }

            List currList = map.get(i);
            if (currList != null)
                currList.addAll(list);
            else
                currList = list;

            map.put(i, currList);
        }

        // Iterate through all elements of map

        Iterator>> iterator = map.entrySet().iterator();

        List visitedKeys = new ArrayList<>();

        List> listSet = new ArrayList<>();

        while (iterator.hasNext()) {
            Entry> entry = iterator.next();
            Integer key = entry.getKey();
            List keyValue = entry.getValue();

            if (visitedKeys.contains(key)) {
                continue;
            }

            Set setItem = new HashSet<>();
            updateSet(key, keyValue, visitedKeys, map, setItem);

            listSet.add(setItem);
        }

        System.out.println("groups=" + listSet);
        System.out.println("Number of groups=" + listSet.size());
    }

    private static void updateSet(Integer key, List keyValue, List visitedKeys,
            HashMap> map, Set setItem) {

        for (Integer item : keyValue) {

            if (visitedKeys.contains(item)) {
                continue;
            }

            if (!item.equals(key)) {
                List mapVal = map.get(item);
                if (mapVal != null) {
                    updateSet(item, mapVal, visitedKeys, map, setItem);
                }
            }

            visitedKeys.add(item);

            setItem.add(item);
        }
    }
}