Subsets - Implementation

Here is the full solution:

function subsets(nums)
    result := []
    backtrack(nums, 0, [], result)
    return result

function backtrack(nums, start, current, result)
    add copy of current to result
    for i from start to length of nums - 1
        add nums[i] to current
        backtrack(nums, i + 1, current, result)
        remove last element from current

Time: $O(n \times 2^n)$ to generate and copy all $2^n$ subsets. Space: $O(n)$ for recursion depth.