Key Idea

Solution 1

• Divide branches into those that include each element as a subset and those that do not.

Solution 2

• Utilize pass-by-value copy of path in DFS for calculations.

Solution 1

def subsets(self, nums: List[int]) -> List[List[int]]:
        subset = []
        def dfs(i):
            if i >= len(nums):
                result.append(subset.copy())
                return

            # decision to include nums[i]
            subset.append(nums[i])
            dfs(i + 1)

            #decision Not to include nums[i]
            subset.pop()
            dfs(i+1)

        result = []
        dfs(0)
        return result

Solution 2

def dfs(start, path):
            result.append(path)

            for i in range(start, len(nums)):
                dfs(i+1, path+[nums[i]])

    result = []
    dfs(0, [])
    return result