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giannitedesco/bfs.py

Last active December 19, 2015 02:38
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Little python library to convert between inorder, BFS and vEB tree layouts. The idea is to do this without constructing any trees. That is to say, in a manner appropriate for implicit layouts, eg. for a database.
Raw
bfs.py
from collections import deque
class Bfs(int):
def left(self):
if self.height == 0:
raise ValueError
return Bfs(self * 2, height = self.height)
def right(self):
if self.height == 0:
raise ValueError
return Bfs(self * 2 + 1, height = self.height)
def parent(self):
if self.height == 0:
raise ValueError
return Bfs(self >> 1, height = self.height)
def __iter__(self):
class BfsIter:
def __init__(self, start):
self.__cur = deque([start])
self.__nxt = deque([])
def next(self, retry = True):
try:
ret = self.__cur.popleft()
try:
self.__nxt.append(ret.left())
self.__nxt.append(ret.right())
except ValueError:
pass
return ret
except IndexError:
if not retry:
raise StopIteration
self.__cur = self.__nxt
self.__nxt = deque([])
return self.next(retry = False)
return BfsIter(self)
def __getitem__(self, compare):
if compare <= 0:
return self.left()
else:
return self.right()
def __new__(cls, *args, **kwargs):
height = kwargs.get('height', 0)
if len(args):
ret = super(Bfs, cls).__new__(cls, args[0])
else:
ret = super(Bfs, cls).__new__(cls, height and 1 or 0)
ret.height = height
if ret > (1 << ret.height):
raise ValueError
return ret
if __name__ == '__main__':
for x in Bfs(3, height = 4):
print x
Raw
inorder.py
from collections import deque
class Inorder(int):
def __ffs(self, i):
ret = 0
while i:
if i & 1:
return ret
i >>= 1
ret += 1
if ret > self.height:
raise ValueError
def rank(self):
return self.height - self.__ffs(self)
def h(self):
return self.__ffs(self) + 1
def left(self):
if self.height == 0:
raise ValueError
s = self.h() - 2
if s < 0:
raise ValueError
return Inorder(self - (1 << s), height = self.height)
def right(self):
if self.height == 0:
raise ValueError
s = self.h() - 2
if s < 0:
raise ValueError
return Inorder(self + (1 << s), height = self.height)
def parent(self):
if self.height == 0:
raise ValueError
s = self.h()
if s < 1:
raise ValueError
x = 1 << s
if self & x:
return Inorder(self - (x >> 1), height = self.height)
else:
return Inorder(self + (x >> 1), height = self.height)
def __iter__(self):
class InorderIter:
def __init__(self, cur, end, h):
self.cur = cur
self.end = end
self.h = h
def next(self):
self.cur += 1
if self.cur >= self.end:
raise StopIteration
return Inorder(self.cur, height = self.h)
s = self.h()
if s < 1:
raise ValueError
x = 1 << (s - 1)
return InorderIter(self - x, self + x, self.height)
def __getitem__(self, compare):
if compare <= 0:
return self.left()
else:
return self.right()
def __new__(cls, *args, **kwargs):
height = kwargs.get('height', 0)
if len(args):
ret = super(Inorder, cls).__new__(cls, args[0])
else:
ret = super(Inorder, cls).__new__(cls, height and \
((1 << height) / 2) or 0)
ret.height = height
if ret < 0 or ret > (1 << ret.height):
raise ValueError
return ret
if __name__ == '__main__':
x = Inorder(height = 4)
print x, x.left(), x.right()
a = x.left().left().parent()
b = x.right().right().parent()
for x in x.right().left():
print '%s -> %s'%(x, x.parent())
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