tasks a-s

Task/Power-set/Python/power-set-1.py

@@ -0,0 +1,20 @@
+def list_powerset(lst):
+    # the power set of the empty set has one element, the empty set
+    result = [[]]
+    for x in lst:
+        # for every additional element in our set
+        # the power set consists of the subsets that don't
+        # contain this element (just take the previous power set)
+        # plus the subsets that do contain the element (use list
+        # comprehension to add [x] onto everything in the
+        # previous power set)
+        result.extend([subset + [x] for subset in result])
+    return result
+
+# the above function in one statement
+def list_powerset2(lst):
+    return reduce(lambda result, x: result + [subset + [x] for subset in result],
+                  lst, [[]])
+
+def powerset(s):
+    return frozenset(map(frozenset, list_powerset(list(s))))

Task/Power-set/Python/power-set-2.py

@@ -0,0 +1,9 @@
+def powersetlist(s):
+    r = [[]]
+    for e in s:
+        print "r: %-55r e: %r" % (r,e)
+        r += [x+[e] for x in r]
+    return r
+
+s= [0,1,2,3]
+print "\npowersetlist(%r) =\n  %r" % (s, powersetlist(s))

Task/Power-set/Python/power-set-3.py

@@ -0,0 +1,25 @@
+def powersequence(val):
+    ''' Generate a 'powerset' for sequence types that are indexable by integers.
+        Uses a binary count to enumerate the members and returns a list
+
+        Examples:
+            >>> powersequence('STR')   # String
+            ['', 'S', 'T', 'ST', 'R', 'SR', 'TR', 'STR']
+            >>> powersequence([0,1,2]) # List
+            [[], [0], [1], [0, 1], [2], [0, 2], [1, 2], [0, 1, 2]]
+            >>> powersequence((3,4,5)) # Tuple
+            [(), (3,), (4,), (3, 4), (5,), (3, 5), (4, 5), (3, 4, 5)]
+            >>>
+    '''
+    vtype = type(val); vlen = len(val); vrange = range(vlen)
+    return [ reduce( lambda x,y: x+y, (val[i:i+1] for i in vrange if 2**i & n), vtype())
+             for n in range(2**vlen) ]
+
+def powerset(s):
+    ''' Generate the powerset of s
+
+        Example:
+            >>> powerset(set([6,7,8]))
+            set([frozenset([7]), frozenset([8, 6, 7]), frozenset([6]), frozenset([6, 7]), frozenset([]), frozenset([8]), frozenset([8, 7]), frozenset([8, 6])])
+    '''
+    return set( frozenset(x) for x in powersequence(list(s)) )

Task/Power-set/Python/power-set-4.py

@@ -0,0 +1,3 @@
+def p(l):
+    if not l: return [[]]
+    return p(l[1:]) + [[l[0]] + x for x in p(l[1:])]