combinations.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class arraycalc {
    public static void main(String[]args){
        List<Integer> arr = Arrays.asList(1,2,3,4,5);
        List<Integer> c = Arrays.asList(4,5);
        List<List<Integer>> result = arraycalc.combinations(arr,c,new ArrayList<Integer>(),new ArrayList<List<Integer>>());
        System.out.println(result);
        System.out.println(combinations(Arrays.asList("A","B","C"),Arrays.asList(2,3),new ArrayList<String>(),new ArrayList<List<String>>()));
    }
    public static  <T> List<List<T>>combinations(List<T> arr,List<Integer> c, List<T> cut, List<List<T>> results){
        if (c.contains(0)){
            List<T>cut3=new ArrayList<T>(cut);
            results.add(cut3);
            if(c.stream().map(x -> x>0).count()==0) {
                return results;
            }
        }
        for(int i=0;i<arr.size();i++){
            List<T> arr2=arr.stream().skip(i+1).collect(Collectors.toList());
            List<T> cut2 = new ArrayList<T>(cut);
            List<Integer> c2=c.stream().map(x->x-1).collect(Collectors.toList());
            cut2.add(arr.get(i));
            results=combinations(arr2,c2,cut2,results);
        }
        return results;
    }
}

// OUTPUT
// [[1, 2, 3, 4], [1, 2, 3, 4, 5], [1, 2, 3, 5], [1, 2, 4, 5], [1, 3, 4, 5], [2, 3, 4, 5]]
// [[A, B], [A, B, C], [A, C], [B, C]]