lettcode 90 子集II

package com.example.lettcode.dailyexercises;

import java.util.*;

/**
 * @Class SubsetsWithDup
 * @Description 90 子集II 
 * 给你一个整数数组 nums ，其中可能包含重复元素，请你返回该数组所有可能的子集（幂集）。
 * 解集 不能 包含重复的子集。返回的解集中，子集可以按 任意顺序 排列。
 * <p>
 * 示例 1：
 * 输入：nums = [1,2,2]
 * 输出：[[],[1],[1,2],[1,2,2],[2],[2,2]]
 * <p>
 * 示例 2：
 * 输入：nums = [0]
 * 输出：[[],[0]]
 * @Author
 * @Date 2021/3/31
 **/
public class SubsetsWithDup {
    /**
     * 方法1：回溯算法
     * 和子集I不同的是，子集II可能出现重复的情况，所以需要去重
     * @param nums
     * @return
     */
    public static List<List<Integer>> subsetsWithDup(int[] nums) {
        if (nums == null || nums.length == 0) return new ArrayList<>();
        // 去重
        Set<List<Integer>> resSet = new HashSet<>();
        resSet.add(new ArrayList<>());
        for (int i = 0; i < nums.length; i++) {
            List<List<Integer>> listList = new ArrayList<>();
            for (List<Integer> integerList : resSet) {
                // 不能直接在List上修改需要复制一份
                List<Integer> integers = new ArrayList<>(integerList);
                integers.add(nums[i]);
                // 排序去重
                Collections.sort(integers);
                listList.add(integers);
            }
            resSet.addAll(listList);
        }

        List<List<Integer>> resList = new ArrayList<>();
        for (List<Integer> integers : resSet) {
            resList.add(integers);
        }
        return resList;
    }
}

// 测试用例
public static void main(String[] args) {
	int[] nums = new int[]{1, 2, 2};
	List<List<Integer>> listList = subsetsWithDup(nums);
	System.out.print("SubsetsWithDup demo01 result:[");
	for (List<Integer> integerList : listList) {
		System.out.print("[");
		for (Integer integer : integerList) {
			System.out.print("," + integer);
		}
		System.out.print("]");
	}
	System.out.println("]");

	nums = new int[]{0};
	listList = subsetsWithDup(nums);
	System.out.print("SubsetsWithDup demo02 result:[");
	for (List<Integer> integerList : listList) {
		System.out.print("[");
		for (Integer integer : integerList) {
			System.out.print("," + integer);
		}
		System.out.print("]");
	}
	System.out.println("]");

	nums = new int[]{4, 4, 4, 1, 4};
	listList = subsetsWithDup(nums);
	System.out.print("SubsetsWithDup demo03 result:[");
	for (List<Integer> integerList : listList) {
		System.out.print("[");
		for (Integer integer : integerList) {
			System.out.print("," + integer);
		}
		System.out.print("]");
	}
	System.out.println("]");
}