```
# Python
from itertools import chain
from collections import deque
class n(object):
left = None
right = None
value = None
def __init__(self, value=None, left=None, right=None):
self.value = value
self.left = left
self.right = right
def __call__(self, left=None, right=None):
self.left = left
self.right = right
return self.value
def preorder(node):
lefts = []
rights = []
if node.left != None:
lefts = preorder(node.left)
if node.right != None:
rights = preorder(node.right)
return chain([node], lefts, rights)
def inorder(node):
lefts = []
rights = []
if node.left != None:
lefts = inorder(node.left)
if node.right != None:
rights = inorder(node.right)
return chain(lefts, [node], rights)
def postorder(node):
lefts = []
rights = []
if node.left != None:
lefts = postorder(node.left)
if node.right != None:
rights = postorder(node.right)
return chain(lefts, rights, [node])
def levelorder(node):
queue = deque([node])
while len(queue) > 0:
node = queue.pop() # Remove from right
yield node
if node.left:
queue.appendleft(node.left)
if node.right:
queue.appendleft(node.right)
# Create nodes
_ = None
A = n('A')
B = n('B')
C = n('C')
D = n('D')
E = n('E')
F = n('F')
G = n('G')
H = n('H')
I = n('I')
# Link the nodes
F(B,G)
B(A,D)
D(C,E)
G(_,I)
I(H,_)
print "Pre order:"
print list(node.value for node in preorder(F))
print "In order:"
print list(node.value for node in inorder(F))
print "Post order:"
print list(node.value for node in postorder(F))
print "Level order (queue):"
print list(node.value for node in levelorder(F))
```