2叉树变双链表

class node:

    def __init__( self , data, left, right):

        self.data = data

        self.left = left

        self.right = right

 

def tree2list(root):

    if root == None :

        return None , None

    if root.left == None and root.right == None:

        return root, root

 

    right = root.right

    head, tail = tree2list(root.left)

   

    tail.right = root

    root.left = tail

   

    head2, tail2 = tree2list(right)

    root.right = head2

    head2.left = root

 

    return head, tail2

 

n1 = node(1, None, None )

n2 = node(2, None, None )

n3 = node(3, n1, n2)

n4 = node(4, None, None )

n5 = node(5, n3, n4)

 

root = n5

head, tail = tree2list(root)

it = head

while it != None:

    print it.data

    it = it.right

 

print "—————"

 

it = tail

while it != None:

    print it.data

    it = it.left