Subsets - Implementation

Here's the complete bitmask solution:

function subsets(nums)
    n := length of nums
    total := 2^n
    result := []
    for mask from 0 to total - 1
        subset := []
        for i from 0 to n - 1
            if (mask & (1 << i)) ≠ 0 then
                append nums[i] to subset
        append subset to result
    return result

Outer loop generates all $2^n$ masks. Inner loop builds each subset by checking which bits are set. Time: $O(n \times 2^n)$ (for each of $2^n$ masks, you check $n$ bits). Space: $O(n \times 2^n)$ for the output.