全排列（可能含重复数字）

class  {
    public List<List<Integer>> permuteUnique(int[] nums) {
        List<List<Integer>> list=new ArrayList<>();
        Arrays.sort(nums);
        backTrack(list,new ArrayList<>(),nums,new boolean [nums.length]);
        return list;
    }
    
    public void backTrack(List<List<Integer>> list,List<Integer> tempList,int [] nums,boolean[] used)
    {
        if(tempList.size()==nums.length)
        {
            list.add(new ArrayList<>(tempList));
        }
        else
        {
            for(int i=0;i<nums.length;i++)
            {
                if(used[i]||(i>0)&&(nums[i]==nums[i-1])&&(!used[i-1])) continue;
                used[i]=true;
                tempList.add(nums[i]);
                backTrack(list,tempList,nums,used);
                used[i]=false;
                tempList.remove(tempList.size()-1);
            }
        }
    }
}