import org.junit.Test;

import java.util.*;

/**

* Created by LXF on 2017/8/12.

*/

public class Main1 {

public List<List<Integer>> subsets(int[] nums) {

List<List<Integer>> list = new ArrayList<>();

Arrays.sort(nums);

backtrack(list, new ArrayList<>(), nums, 0);

return list;

}

void backtrack(List<List<Integer>> list , List<Integer> tempList, int [] nums, int start) {

list.add(new ArrayList<>(tempList));

for (int i = start; i < nums.length; i++) {

tempList.add(nums[i]);

backtrack(list, tempList, nums, i + 1);

tempList.remove(tempList.size() - 1);

}

}

@Test

public void test() {

List<List<Integer>> result = subsets(new int[]{1, 2, 3, 4});

System.out.println(result);

}

}