Given a string array split array into all combinations of subset group so that each group having same number of elements as in given array

Given a array of String values split array with all possible combibantions of group of subset's as 
given inputs:-

 String[] items = {"a","b","c","d"};  asume items array elements are an cart item ids like "a" might be equal to in real senorio "ab2fdsde23d2$sad"	

I have to fulfil orders from FCs(any store or warehouse) so I wanted to split items with all subset combinations(as Given below) to get fulfilment centres with less cost where I can find all items.   

so please help me to get optimum solution to get this output
//output:- 
[ [a, b, c, d] ,
[a, b, c] [d] ,
[a, b, d] [c] ,
[a, b] [c, d] ,
[a, c, d] [b] ,
[a, c] [b, d] ,
[a, d] [b, c] ,
[a] [b, c, d] ,
[a, b] [c] [d] ,
[a, c] [b] [d] ,
[a] [b, c] [d] ,
[a, d] [b] [c] ,
[a] [b, d] [c] ,
[a] [b] [c, d] ,
[a] [b] [c] [d]  ]

example2 :-

String[] arr ={"a","b","c"};

output :- [
        [[a], [b], [c] ] ,
        [[a,b],[c]] ,
        [[a,c],[b] ] ,
        [[b,c],[a] ]
        [a,b,c,d]
      ] ;

For more reference, I can tell you  if you have 4 items in the cart like a,b,c,d so to fulfil these items from any of fulfilment centres (FCs) by splitting product in any combinations


please check the below-given solution and optimise it if you guys can.

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;

import org.model.Item;

public class TestMain2 {

	public static void main(String[] args) {
		// first param itemid and second quantity
		Item item1 = new Item("a", 1);
		Item item2 = new Item("b", 18);
		Item item3 = new Item("c", 3);
		Item item4 = new Item("d", 1);
		List<Item> items = new ArrayList<>();
		items.add(item1);
		items.add(item2);
		items.add(item3);
		items.add(item4);
		
		int itemsCount = items.size();
		String[] arr = new String[itemsCount] ;
		for(int i=0 ; i<items.size() ; i++) {
			arr[i] = items.get(i).getItemId();
		}
		
		List<List<List<String>>> resItemSubsetGroup = new ArrayList<>();
		for(int i=1 ; i<=items.size() ; i++) {
			partitionsItemListInKSubsets(arr, itemsCount, i,resItemSubsetGroup);
		}
		
		for(List<List<String>> subsetGroup:resItemSubsetGroup) {
			
			for(List<String> ls:subsetGroup) {
				System.out.print(ls+" ");
			}
			System.out.println();
		}
		
	}
	
	 static void PartitionSub(String arr[], int i,
             int N, int K, int nos,
             List<List<String>> v , List<List<List<String>>> resItemSubsetGroup)
		{
		

		if (i >= N)
		{
		
		if (nos == K)
		{
		List<List<String>> lls = new ArrayList<>();
		
		for(List<String> ls:v) {
		
		List<String> lsnew = new ArrayList<>();
		
		for(String l:ls) {
			  lsnew.add(l);
		}
		lls.add(lsnew);
		}
		
		resItemSubsetGroup.add(lls);
		}
		return ;
		}
		
		for (int j = 0; j < K; j++)
		{
		
		if (v.get(j).size() > 0)
		{
		v.get(j).add(arr[i]);
		
		PartitionSub(arr, i + 1, N, K, nos, v ,resItemSubsetGroup);
		v.get(j).remove(v.get(j).size()-1);
		}
		
		else
		{
		
		v.get(j).add(arr[i]);
		PartitionSub(arr, i + 1, N, K, nos + 1, v , resItemSubsetGroup);
		v.get(j).remove(v.get(j).size()-1);
		
		break;
		}
		}
		}
		
		static List<List<List<String>>> partitionsItemListInKSubsets(String arr[], int N, int K ,List<List<List<String>>> resItemSubsetGroup)
		{
		List<List<String>> v = new ArrayList<>();
		
		for(int i = 0; i < K; i++)
		v.add(new ArrayList<>());
		
		if (K == 0 || K > N)
		{
		System.out.println("Not possible");
		}
		else
		{
		PartitionSub(arr, 0, N, K, 0, v,resItemSubsetGroup);
		}
		
		return resItemSubsetGroup;
		}
}