Permutations II

 1 class Solution {
 2     /**
 3      * @param nums: A list of integers.
 4      * @return: A list of unique permutations.
 5      */
 6     public ArrayList<ArrayList<Integer>> permuteUnique(ArrayList<Integer> nums) {
 7         ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
 8         ArrayList<Integer> list = new ArrayList<Integer>();
 9         if(nums == null || nums.size() == 0) {
10             return result;
11         }
12         
13         Collections.sort(nums);
14         boolean[] visited = new boolean[nums.size()];
15         permuteUniqueHelper(result, list, nums, visited);
16         return result;
17     }
18     
19     public void permuteUniqueHelper(ArrayList<ArrayList<Integer>> result,
20                               ArrayList<Integer> list,
21                               ArrayList<Integer> nums,
22                               boolean[] visited) {
23         if(list.size() == nums.size()) {
24             result.add(new ArrayList<Integer>(list));
25         }
26         
27         for(int i = 0; i < nums.size(); ++i) {
28             if(visited[i] || (i > 0 && nums.get(i) == nums.get(i - 1) && !visited[i - 1]))
29                 continue;
30                 
31             visited[i] = true;    
32             list.add(nums.get(i));
33             permuteUniqueHelper(result, list, nums, visited);
34             list.remove(list.size() - 1);
35             visited[i] = false;
36         }
37     }
38 }