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] ]Solution:
public List<List<Integer>> permuteUnique(int[] nums) { List<List<Integer>> list = new ArrayList<>(); Arrays.sort(nums); backtrack(list, new ArrayList<>(), nums, new boolean[nums.length]); return list; } private void backtrack(List<List<Integer>> list, List<Integer> tempList, int[] nums, boolean[] used) { if (tempList.size() == nums.length) { list.add(new ArrayList<>(tempList)); } else { for (int i = 0; i < nums.length; i++) { if (used[i] || (i > 0 && nums[i] == nums[i - 1] && !used[i - 1])) continue; used[i] = true; tempList.add(nums[i]); backtrack(list, tempList, nums, used); used[i] = false; tempList.remove(tempList.size() - 1); } } }