Leetcode -- permutations II

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], And[2,1,1].

Original question link: https://oj.leetcode.com/problems/permutations-ii/

Question: given a set of repeated elements, all possible independent arrays are returned.

Idea: you only need to modify the full sorting of the previous question. First, sort the array. In this way, the same elements are adjacent, if the front and back elements are the same, the same value is skipped.

public List<List<Integer>> permuteUnique(int[] num) {if (num == null)return null;List<List<Integer>> result = new ArrayList<List<Integer>>();if (num.length == 0)return result;Arrays.sort(num);permute(num, new boolean[num.length], new ArrayList<Integer>(), result);return result;}public void permute(int[] num, boolean[] isused,ArrayList<Integer> current, List<List<Integer>> result) {if (current.size() == num.length) {result.add(new ArrayList<Integer>(current));return;}for (int i = 0; i < num.length; i++) {if (!isused[i]) {isused[i] = true;current.add(num[i]);permute(num, isused, current, result);isused[i] = false;current.remove(current.size() - 1);while (i + 1 < num.length && num[i + 1] == num[i])i++;}}}

Leetcode -- permutations II