Perfect Friends

I/P:

7

5

0 1

2 3

4 5

5 6

4 6

O/P: 16

Step 1. Find connected components of graph

Step 2.  Using for loop, find pairing combinations

package pep.Day39;

import java.io.*;
import java.util.*;

public class Perfect_Friends {
    static class Edge {
        int src;
        int nbr;

        Edge(int src, int nbr) {
            this.src = src;
            this.nbr = nbr;
        }
    }

    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        int vtces = Integer.parseInt(br.readLine());
        ArrayList<Edge>[] graph = new ArrayList[vtces];
        for (int i = 0; i < vtces; i++) {
            graph[i] = new ArrayList<>();
        }

        int edges = Integer.parseInt(br.readLine());
        for (int i = 0; i < edges; i++) {
            String[] parts = br.readLine().split(" ");
            int v1 = Integer.parseInt(parts[0]);
            int v2 = Integer.parseInt(parts[1]);
            graph[v1].add(new Edge(v1, v2));
            graph[v2].add(new Edge(v2, v1));
        }

        boolean[] visited = new boolean[vtces];
        ArrayList<ArrayList<Integer>> comps = new ArrayList<>();
        ArrayList<Integer> comp;
        for (int i = 0; i < vtces; i++) {
            if (!visited[i]) {
                comp = new ArrayList<>();
                dfs(graph, i, visited, comp);
                comps.add(comp);
            }
        }

        int size = 0;
        for (int i = 0; i < comps.size(); i++) {
            for (int j = i+1; j < comps.size(); j++) {
                size += (comps.get(i).size() * comps.get(j).size());
            }
        }

        System.out.println(size);
    }

    private static void dfs(ArrayList<Edge>[] graph, int src, boolean[] visited, ArrayList<Integer> comp) {
        visited[src] = true;
        comp.add(src);
        for (Edge e : graph[src]) {
            if (!visited[e.nbr]) {
                dfs(graph, e.nbr, visited, comp);
            }
        }
    }

}