Given a collection of numbers that might contain duplicates, return all possible unique permutations.
For example,[1,1,2] have the following unique permutations:
[ [1,1,2], [1,2,1], [2,1,1] ]
1 public class Solution { 2 List<List<Integer>> ans = new ArrayList<List<Integer>>(); 3 public List<List<Integer>> permuteUnique(int[] nums) { 4 List<Integer> list = new ArrayList<Integer>(); 5 boolean[] visit = new boolean[nums.length]; 6 Arrays.sort(nums); 7 DFS(list,nums,visit); 8 return ans; 9 } 10 11 public void DFS(List<Integer> list, int[] nums, boolean[] visit){ 12 if(list.size() == nums.length){ 13 ans.add(list); 14 return; 15 } 16 17 for(int i = 0; i < nums.length; i++){ 18 if(visit[i] || (i>0 && nums[i] == nums[i-1] && !visit[i-1])) continue; 19 visit[i] = true; 20 List<Integer> tmp = new ArrayList<>(list); 21 tmp.add(nums[i]); 22 DFS(tmp,nums,visit); 23 visit[i] = false; 24 } 25 } 26 }