Permutations II

 1 public class Solution {
 2     public ArrayList<ArrayList<Integer>> permuteUnique(int[] num) {
 3         // IMPORTANT: Please reset any member data you declared, as
 4         // the same Solution instance will be reused for each test case.
 5         int len = num.length;
 6         ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
 7         HashSet<ArrayList<Integer>> tmpResult = new HashSet<ArrayList<Integer>>();
 8         permutation(num, 0, len, result, tmpResult);
 9         return result;
10     }
11     
12     public void permutation(int[] num, int depth, int len, ArrayList<ArrayList<Integer>> result, HashSet<ArrayList<Integer>> tmpResult){
13         
14         if(depth == len){
15             ArrayList<Integer> per = new ArrayList<Integer>();
16             for(int i =0 ; i < len; i++)
17                 per.add(num[i]);
18                 
19             if(tmpResult.add(per))
20                 result.add(per);
21         }
22         
23         for(int i = depth; i < len; i++) {
24             if(i != depth && num[i] == num[depth])
25                 continue;
26 
27             int tmp = num[i];
28             num[i] = num[depth];
29             num[depth] = tmp;
30             
31             permutation(num, depth + 1, len, result, tmpResult);
32             
33             tmp = num[i];
34             num[i] = num[depth];
35             num[depth] = tmp;
36         }
37     }
38 }