题解 | #有重复项数字的全排列 TreeSet#

import java.util.*;

public class Solution {
    public ArrayList<ArrayList<Integer>> permuteUnique(int[] num) {
        if (num == null || num.length == 0){
            return new ArrayList<>();
        }
        TreeSet<ArrayList<Integer>> set = new TreeSet<>(new Comparator<ArrayList<Integer>>() {
            @Override
            public int compare(ArrayList<Integer> o1, ArrayList<Integer> o2) {
                for (int i = 0; i < o1.size(); i++) {
                    if (o1.get(i) != o2.get(i)) return o1.get(i) - o2.get(i);
                }
                return 0;
            }
        });
        process(num, 0, set);
        return new ArrayList<>(set);
    }
    public static void process(int[] num, int index, TreeSet<ArrayList<Integer>> set){
        if (index == num.length){
            ArrayList<Integer> list = new ArrayList<>();
            for (int i : num) {
                list.add(i);
            }
            set.add(list);
            return;
        }
        for (int i = index; i < num.length; i++) {
            swap(num, index, i);
            process(num, index + 1, set);
            swap(num, index, i);
        }
    }
    public static void swap(int[] num, int i, int j){
        int temp = num[i];
        num[i] = num[j];
        num[j] = temp;
    }
}