I was just playing around in python trying to get a basic sort of linked list working. I was able to make a simple linked list using an article I read online that looks like this:
class node:
def __init__(self, value = None, next = None):
self.value = value
self.next = next
def printList(node):
print "[",
while node:
print node,
node = node.next
print "]"
def printBackward(list):
if list == None:
return
head = list
tail = list.next
printBackward(tail)
print head,
def removeSecond(list):
if list == None:
return
first = list
second = list.next
#Make the first node refer to the third
first.next = second.next
# seperate the second node from the rest of the list
second.next = None
return secondThat just allowed you to make a linked list and remove some elements or print it backwards, simple things like that.
EX:
>>> node1 = node(1)
>>> node2 = node(2)
>>> node3 = node(3)
>>> node1.next = node2
>>> node2.next = node3
>>> printList(node1)
[ 1 2 3 ]
>>>
>>> printBackward(node1)
3 2 1
The problem is that I start to get confused when trying to add elements to the start of the list. I tried to keep using the node class but then add in a linkedList class and an addFirst function, as well as a new function to print the list.
I came up with this:
class node:
def __init__(self, value = None, next = None):
self.value = value
self.next = next
def __str__(self):
return str(self.value)
class linkedList:
def __init__(self):
self.length = 0
self.head = None
def addFirst(list,value):
first = node(value)
if list.head != None:
second = list.head
first.next = second
list.head == first
list.length += 1
def printlst(list):
print "[",
cursor = list.head
while cursor != None:
print cursor.value
cursor = cursor.next
print "]"I trid to run it by doing something like
>>>newList = linkedList()
>>> addFirst(newList,4)
>>> printlst(newList)
[]
Whenever I try that it always just returns me those brackets and I don't quite understand why. If someone could help me figure out a way to set up a linked list and add or remove elements from it without making a specific instance like the "removeSecond" above then I'd really appreciate it.
Also: I've looked into making everything a method and I was not able to figure out what to do, so I'd prefer if someone could explain it in a way that doesn't involve the add functions being methods. Of course you can still give a shot at explaining it to me if you want to.
Thanks for any help in advance.
