回溯法4,排列问题，带条件

 1 public class Solution {
 2     public static void main(String[] args) {
 3        int[] arr = new int[]{1,2,2};
 4         Arrays.sort(arr);
 5         ArrayUtils.displayArrayList(permuteUnique(arr));
 6     }
 7 
 8     public static List<List<Integer>> permuteUnique(int[] nums) {
 9         List<List<Integer>> result = new ArrayList<>();
10         boolean[] usedTable = new boolean[nums.length];
11         backTrace(result,new ArrayList<>(),nums,usedTable);
12 
13         return result;
14     }
15 
16     private static void backTrace(List<List<Integer>> result,List<Integer> list,int[] nums,boolean[] used){
17         if(list.size() == nums.length){
18             result.add(new ArrayList<>(list));
19             return;
20         }
21 
22         for (int i = 0; i < nums.length; i++) {
23             if(used[i]){
24                 continue;
25             }
26             if( i>=1 && !used[i-1] && !used[i] && nums[i]==nums[i-1]){
27                 continue;
28             }
29             list.add(nums[i]);
30             used[i] = true;
31             backTrace(result,list,nums,used);
32             list.remove(list.size()-1);
33             used[i] = false;
34         }
35     }
36 }