Need help in Java

general
1

I want map integer to vector in java…

for example in c++ we use → map< int, vector > can we do this in java if Yes… then How?

2 
import java.util.*;
public class Main
{
	public static void main(String[] args) {
		Map<Integer, Vector<Integer>> my_map = new HashMap<>();
		my_map.put(1, new Vector<Integer>());
		my_map.get(1).add(1);
		my_map.get(1).add(2);
		
		// Nullpointer exception
		// my_map.get(2).add(1);
		System.out.println(my_map);
		
		my_map.put(2, new Vector<Integer>());
		my_map.get(2).add(5);
		
		System.out.println(my_map);
	}
}

Output

{1=[1, 2]}
{1=[1, 2], 2=[5]}

You can also use loops to insert, but make sure the key is present.

3

thank You so much for your help

4

You can do something like this

Map<Integer,ArrayList<Integer>> mp = new HashMap<>();

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

                    if(!mp.containsKey(i)){

                        mp.put(i, new ArrayList<Integer>());

                    }

                    mp.get(i).add(i);

                }

I hope it helps