Q3 Number of Operations to Make Network Connected - LeetCode 1319

class Solution {
    public int makeConnected(int n, int[][] connections) {
        //edge case - if we are given less than n-1 nodes to connect n nodes

        if(connections.length < n-1)
        return -1;

        /* 
        find no. of components in the graph(c) and assume them to be an 
        individual node , therefore we will need c-1 edges to connect them
        */
        int c = 0;

        //make a graph using HM
        HashMap<Integer,ArrayList<Integer>> graph = new HashMap<>();
        
        for(int connection[] : connections){
            int a = connection[0] , b = connection[1];

            graph.computeIfAbsent(a , k -> new ArrayList<>()).add(b);
            graph.computeIfAbsent(b , k -> new ArrayList<>()).add(a);
        }
        
        System.out.println(graph);
        //visited array 
        boolean visited[] = new boolean[n];
        
        //finding all components by using dfs on every node

        for(int i =0 ; i < n ; i++){

            if(visited[i] == false){
                
                if(graph.containsKey(i))
                dfs(graph , i , visited);

                c++;

            }
            
        }

        return c - 1;

        
    }

    public void dfs (HashMap<Integer,ArrayList<Integer>> graph , int source , 
    boolean[] visited ){

        
        visited[source] = true;

        for(int edge : graph.get(source)){
            if(visited[edge] == false)
            dfs(graph , edge , visited);
        }

        return ;
    }






}