Python实现求一个集合所有子集的示例

def PowerSetsRecursive(items):

  """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 sebset that contains the first_elt

  for partial_sebset in PowerSetsRecursive(rest_list):

    subsets.append(partial_sebset)

    next_subset = partial_sebset[:] +[first_elt]

    subsets.append(next_subset)

  return subsets

def PowerSetsRecursive2(items):

  # the power set of the empty set has one element, the empty set

  result = [[]]

  for x in items:

    result.extend([subset + [x] for subset in result])

  return result

def PowerSetsBinary(items):

  #generate all combination of N items

  N = len(items)

  #enumerate the 2**N possible combinations

  for i in range(2**N):

    combo = []

    for j in range(N):

      #test jth bit of integer i

      if(i >> j ) % 2 == 1:

        combo.append(items[j])

    yield combo