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treeset.py
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treeset.py
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# -*- Mode: Python -*-
# set operations on avl trees.
import avl
def intersection (a, b):
ta = avl.newavl(a)
result = avl.newavl()
for x in b:
if ta.has_key (x):
result.insert (x)
ta.remove (x)
return result
def union (a, b):
result = avl.newavl(a)
for key in b:
if not a.has_key(key):
result.insert(key)
return result
def difference (a, b):
result = avl.newavl(a)
for key in b:
if a.has_key (key):
result.remove (key)
return result
# an abstract set implementation based on avl trees
class avl_set:
"accepts an optional list or set as an initializer"
def __init__ (self, set=None):
if set == None:
self.items = avl.newavl()
elif type(set) == type([]):
self.items = avl.newavl(set[:])
elif type(set) == type(self):
self.items = avl.newavl(set.items)
else:
self.items = avl.newavl(set)
def add (self, item):
if not self.items.has_key (item):
self.items.insert(item)
else:
raise ValueError, "item already present in set"
def remove (self, item):
if self.items.has_key (item):
self.items.remove(item)
else:
raise ValueError, "item not in set"
def has_item (self, item):
return self.items.has_key (item)
# addition == union
def __add__ (self, other):
return self.__class__ (union (self.items, other.items))
# subtraction == difference
def __sub__ (self, other):
return self.__class__ (difference (self.items, other.items))
# multiplication == intersection
def __mul__ (self, other):
return self.__class__ (intersection (self.items, other.items))
# comparison: expresses the <subset> relation, a <= b
def __cmp__ (self, other):
# is <a> a proper subset of <b> ?
# -1 == no
# +1 == yes
# 0 == they are equal (improper)
if len(self.items) > len(other.items):
return -1
result = 0
for x in self.items:
if not other.items.has_key (x):
return -1
if len(self.items) == len(other.items):
return 0
else:
return 1
def __repr__ (self):
return '{' + repr(self.items)[1:-1] + '}'