Python求一个集合的所有子集算法对比时间最短

import datetime
def PowerSetsBinary(items):#1，二进制方法
    N = len(items)
    # generate all combination of N items
    # enumerate the 2**N possible combinations
    res=[]
    for i in range(2 ** N):
        combo = []
        for j in range(N):  # jth bit of Integer i
            if (i >> j) % 2 == 1:
                combo.append(items[j])
        res.append(combo)
    return res

def PowerSetsRecursive(items):#2，回归方法
    """Use recursive call to return all subsets of items, include empty set"""

    if len(items) == 0:
        # if the lsit is empty, return the empty list
        return [[]]

    subsets = []
    first_elt = items[0]  # first element
    rest_list = items[1:]

    # Strategy: Get all subsets of rest_list;
    # for each of those subsets,a full subset list will contain both the original subset
    # as well as a version of the subset that contains the first_elt(according to my a_2 思路,you will understand this)

    for partial_subset in PowerSetsRecursi