Find all permutations of given items using Java 8

Permutations.java

public class Permutations {

    public static <T> Stream<Stream<T>> of(final List<T> items) {
        return IntStream.range(0, factorial(items.size())).mapToObj(i -> permutation(i, items).stream());
    }

    private static int factorial(final int num) {
        return IntStream.rangeClosed(2, num).reduce(1, (x, y) -> x * y);
    }

    private static <T> List<T> permutation(final int count, final LinkedList<T> input, final List<T> output) {
        if (input.isEmpty()) { return output; }

        final int factorial = factorial(input.size() - 1);
        output.add(input.remove(count / factorial));
        return permutation(count % factorial, input, output);
    }

    private static <T> List<T> permutation(final int count, final List<T> items) {
        return permutation(count, new LinkedList<>(items), new ArrayList<>());
    }

}

Permutations.of(Arrays.asList(1, 2, 3)).forEach(p -> { p.forEach(System.out::print); System.out.print(" "); });

will return:
123 132 213 231 312 321

Hey, can you please tell me which packages I have to include? It does´nt run on my Java.

import java.util.stream.*;

Great code, note that if you have 13 or more items the code will silently break - use replace 'int' with 'long':

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.stream.LongStream;
import java.util.stream.Stream;

/**
*

• @author simon
  */
  public class Permutations2
  {
  public static Stream<Stream> of(final List items)
  {
  return LongStream.range(0, factorial(items.size())).mapToObj(i -> permutation(i, items).stream());
  }

  private static long factorial(final int num)
  {
  return LongStream.rangeClosed(2, num).reduce(1L, (x, y) -> x * y);
  }

  private static List permutation(final long count, final LinkedList input, final List output)
  {
  if (input.isEmpty()) { return output; }

   final long factorial = factorial(input.size() - 1);
   output.add(input.remove((int)(count / factorial)));
   return permutation(count % factorial, input, output);
  

  }

  private static List permutation(final long count, final List items)
  {
  return permutation(count, new LinkedList<>(items), new ArrayList<>());
  }
  }

How to generate all permutations of 2 lists?

Permutations.of(list1, list2)

Thank you