递归

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定,请勿修改,直接返回方法规定的值即可
     *
     * 
     * @param num int整型一维数组 
     * @return int整型ArrayList<ArrayList<>>
     */
    ArrayList<ArrayList<Integer>> res=new ArrayList<>();
    public ArrayList<ArrayList<Integer>> permute (int[] num) {
        // write code here
        LinkedList<Integer> list=new LinkedList<>();
        backTrack(num,list);

        return res;
    }
    public  void backTrack(int[] num,LinkedList<Integer> list){
        if(list.size()==num.length){
            res.add(new ArrayList<Integer>(list));
            return ;
        }
        for(int i=0;i<num.length;i++){
            if(list.contains(num[i])){
                continue;
            }
            list.add(num[i]);
            backTrack(num,list);
            list.removeLast();
        }

    }
}