1 public class Solution {
 2     public ArrayList<ArrayList<Integer>> permute(int[] num) {
 3         int len = num.length;
 4         ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
 5         if(len<=0) return res;
 6         boolean [] visited = new boolean[len];
 7         get(res,new ArrayList<Integer>(),0,num,visited);
 8         return res;
 9     }
10     public void get(ArrayList<ArrayList<Integer>> res,ArrayList<Integer>output,int depth,int []num,boolean []visited){
11         if(depth==num.length){
12             ArrayList<Integer> temp = new ArrayList<Integer>();
13             temp.addAll(output);
14             res.add(temp);
15             return;
16         }
17         for(int i=0;i<num.length;i++){
18             if(!visited[i]){
19                 visited[i]=true;
20                 output.add(num[i]);
21                 get(res,output,depth+1,num,visited);
22                 output.remove(output.size()-1);
23                 visited[i] = false;
24             }
25         }
26     }
27 }