[Leetcode] 47. 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]

.

import java.util.ArrayList;
public class Solution {
public List<List<Integer>> permuteUnique(int[] num) {
ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
if(num == null || num.length == 0) return result;
ArrayList<Integer> list = new ArrayList<Integer>();
boolean[] visited = new boolean[num.length];
helper(num, result, list, visited);
return result;
}
private void helper(int[] num, ArrayList<ArrayList<Integer>> result, ArrayList<Integer> list, boolean[] visited){
if(list.size() == num.length){
result.add(new ArrayList<Integer>(list));
return;
}
for(int i = 0; i < num.length; i++){
if(visited[i] || (i > 0 && num[i] == num[i - 1] && !visited[i - 1])){
continue;
}
list.add(num[i]);
visited[i] = true;
helper(num, result, list);
list.remove(list.size() - 1);
visitied[i] = false;
}
}
}