from copy import deepcopy
class Solution:
    '''
    NOT THE  MOST EFFICIENT SOLUTION
    '''
    def subsets(self, nums: List[int]) -> List[List[int]]:
        output = [[]]
        for n in nums:
            l = len(output)
            output = output + deepcopy(output)
            for i in range(l):
                output[i].append(n)
        return output

public List<List<Integer>> subsets(int[] nums) {
    List<List<Integer>> output = new ArrayList<>();
    output.add(new ArrayList<Integer>());
    for(Integer n: nums) {
        int l = output.size();
        for(int i=0; i<l; i++) {
            List<Integer> newList = new ArrayList<>(output.get(i));
            newList.add(n);
            output.add(newList);
        }
    }
    return output;
}