Subsets.java

package com.company;

import org.junit.Test;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Subsets {
    public List<List<Integer>> subsets(int[] nums) {
        List<List<Integer>> list = new ArrayList<>();
        Arrays.sort(nums);
        backtrack(list, new ArrayList<>(), nums, 0);
        return list;
    }

    private void backtrack(List<List<Integer>> list,
                           List<Integer> tmpList,
                           int[] nums,
                           int start) {
        list.add(new ArrayList<>(tmpList));
        for (int i = start; i < nums.length; i++) {
            tmpList.add(nums[i]);
            backtrack(list, tmpList, nums, i + 1);
            tmpList.remove(tmpList.size() - 1);
        }
    }

    @Test
    public void test() {
        List<List<Integer>> subsetsLists = subsets(new int[]{1, 2, 3});
        for (List<Integer> list : subsetsLists) {
            for (Integer a : list) {
                System.out.print(a + " ");
            }
            System.out.println();
        }
    }
}