1. Python LinkedLists

2. LinkedList Code from class on Thursday September 19, 2013
element
Node
size
LinkedList
next 1
head 1
tail 1 n1
ll1
element = “a”
next = None
size = 0
head = n2
tail = n1
element = “b”
next = n1 n2
class LinkedList() :
head = None
tail = None
size = 0
def cons(self, val) :
n = Node(val)
self.size+=1
if self.head == None :
self.head = n
self.tail = n
else :
n.next = self.head
return self
def car(self) :
return self.head.element
def cdr(self) :
l = self
if self.size > 0 :
l.head = l.head.next
l.size -= 1
return l
def __str__(self):
result = "'("
current = self.head
for i in range(self.size+1):
if current != None:
result += str(current.element)
if current.next != None :
result += ", " # Separate two elements with a comma
current = current.next
else:
result += ")" # Insert the closing ] in the string
return result
# Return an iterator for a linked list
def __iter__(self): # To be discussed in Section 18.3
return LinkedListIterator(self.head)
# The Node class
class Node:
def __init__(self, element):
self.element = element
self.next = None
class LinkedListIterator: # To be discussed in Section 18.3
def __init__(self, head):
self.current = head
def next(self):
if self.current == None:
raise StopIteration
element = self.current.element
self.current = self.current.next
return element
ll1 = LinkedList()
n1 = Node("a")
ll1.head = n1
ll1.tail = n1
ll1.size+=1
print "ll1 is: ", ll1
n2 = Node("b")
ll1.head = n2
n2.next = n1
Gives:
ll1 is: '(a)
ll1 is: '(b, a)
See the class calendar for a larger font size version of this code.