java实现没有重复数字的全排列

import java.util.*;

public class Solution {
     ArrayList>arrayList=new ArrayList<>();
    public ArrayList> permute(int[] num) {
        Arrays.sort(num);
        ArrayLista=new ArrayList<>();
        bl(num,a);
        return arrayList;
    }
     private void bl(int[] num, ArrayList a) {
        if (a.size()==num.length){
            arrayList.add(new ArrayList<>(a));
            return;
        }
        for (int i=0;i