Subset

class Solution:

    def subsets(self, nums):

        """

        :type nums: List[int]

        :rtype: List[List[int]]

        """

        res = [[]]

        for num in nums:

            res += [item+[num] for item in res]

        return res

class Solution {

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

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

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

        return list;

    }

    public void subset(List<List<Integer>> lists, List<Integer> temp, int[] nums, int index) {

        lists.add(new ArrayList<>(temp));

        if(index == nums.length) {

            return;

        }

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

            temp.add(nums[i]);

            subset(lists, temp, nums, i+1);

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

        }

    }

}

class Solution:

    def subsets(self, arr):

        """

        :type nums: List[int]

        :rtype: List[List[int]]

        """

        list = []

        temp = []

        return self.helper(list, temp, arr, 0)

    def helper(self, list, temp ,arr, size):

        list.append(temp[0:len(temp)])

        if(size >= len(arr)):

            return list

        for i in range(size, len(arr)):

            temp.append(arr[i])

            self.helper(list, temp, arr, i+1)

            temp.remove(temp[len(temp)-1])

        return list