arrangement of different items in a set in java

Question

Like I have a List {Pie,Pudding,Pancake,Jelly,SpongeCake}

I want to find all the possible arrangements of this list like {Pudding,Pancake,SpongeCake,Jelly,Pie} . . . . . . So on I am facing trouble because I want to make this code generic.

Answer 1

try this:

import java.util.ArrayList;
import java.util.Arrays;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
public class So23034581 {
    public static List<List<Integer>> permutations(int n) { // could these be
        // sets?
        final List<List<Integer>> v=new ArrayList<>();
        if(n<=1) {
            List<Integer> a=new ArrayList<>(1);
            a.add(0);
            v.add(a);
        } else {
            final List<List<Integer>> v1=permutations(n-1);
            int nMius1Factorial=v1.size();
            for(int i=0;i<nMius1Factorial;i++) {
                List<Integer> a=v1.get(i);
                Integer[] aa=a.toArray(new Integer[0]);
                for(int j=0;j<n;j++) { // copy a, inserting n at a2[j]
                    Integer[] a2a=new Integer[n];
                    // System.out.println("size of a: "+a.size());
                    // System.out.println("size of a2: "+a2a.length);
                    // System.out.println("j="+j);
                    System.arraycopy(aa,0,a2a,0,j);
                    a2a[j]=n-1;
                    // System.out.println("j="+j+", j+1="+(j+1)+", n="+(n-j-1));
                    System.arraycopy(aa,j,a2a,j+1,n-j-1);
                    v.add(Arrays.asList(a2a));
                }
            }
        }
        return v;
    }
    public static void main(String[] arguments) {
        LinkedHashSet<String> set=new LinkedHashSet<>(Arrays.asList(new String[]{"Pie","Pudding","Pancake","Jelly","SpongeCake"}));
        List<List<Integer>> permutations=permutations(set.size());
        List<String> l=new ArrayList<>(set);
        for(List<Integer> p:permutations) {
            for(int i=0;i<p.size();i++)
                System.out.print(l.get(p.get(i))+" ");
            System.out.println();
        }
    }
}