LeetCode-permutations-ii

Given a collection of numbers that might contain duplicates, return all possible unique permutations.

For example,
[1,1,2]have the following unique permutations:
[1,1,2],[1,2,1], and[2,1,1].

import java.util.*;
public class Solution {
 
    public ArrayList<ArrayList<Integer>> permuteUnique(int[] num) {
 
        ArrayList<ArrayList<Integer>> list = new ArrayList<>();
 
        ArrayList<Integer> temp = new ArrayList<>();
 
        boolean[] book = new boolean[num.length];
 
        Arrays.sort(num);
 
        dfs(list,temp,0,num,book);
 
        return list;
 
    }
 
          
 
    public void dfs(ArrayList<ArrayList<Integer>> list,ArrayList<Integer> temp,int step,int[] num,boolean[] book){
 
        if(step==num.length){
            list.add(new ArrayList<>(temp));
              return;
 
        }
 
        for(int i=0;i<num.length;i++){
 
            if(!book[i]){
 
                book[i] = true;
 
                temp.add(num[i]);
 
                dfs(list,temp,step+1,num,book);
 
                temp.remove(temp.size()-1);
 
                book[i] = false;
 
                while(i<num.length-1 && num[i]==num[i+1]) i++;
 
            }
 
        }
 
    }
 }