Permutations II.java

public class Solution {
    public ArrayList<ArrayList<Integer>> permuteUnique(int[] num) {
        // Start typing your Java solution below
        // DO NOT write main() function
         return permutation( num, num.length-1, new HashSet<ArrayList<Integer>>()); 
    }
     ArrayList<ArrayList<Integer>> permutation(int [] num, int end, HashSet<ArrayList<Integer>> set)
    {
        ArrayList<ArrayList<Integer>> result=new ArrayList<ArrayList<Integer>> (); 
        if(end<0)
        {
        result.add(new ArrayList<Integer>());
        return result; 
        }
        int rest=num[end]; 
        ArrayList<ArrayList<Integer>> subResult=permutation(num, end-1, set);
        for(ArrayList<Integer> list: subResult)
        {
            int size=list.size(); 
            for(int i=0; i<=size; i++)
            {
                list.add(i, rest);
                if(!set.contains(list))
                {
                   result.add((ArrayList<Integer>)list.clone()); 
                   set.add((ArrayList<Integer>)list.clone());
                }            
                list.remove(i);
            }
        }
        return result; 
    }
}