Python实现求一个集合所有子集的示例

方法一：回归实现

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

方法二：二进制法

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