问题
So I'm learning Linked Lists in Python but having trouble inserting a node between my nodes. Let me post my code below and explain what I've done and where I believe the problem is happening.
class Node(object):
def __init__(self, data):
self.data = data
self.nextNode = None
'''
def __str__(self):
return str(self.data)
'''
class LinkedList(object):
def __init__(self):
self.head = None
self.tail = None
# Insert inbetween
def insert_in_between(self, data, prev_data):
print("<<< INSERT INBETWEEN >>>")
# instantiate the new node
new_node = Node(data)
print("This is new_node: ", new_node)
# assign to head
thisval = self.head
print("This is thisval: ", thisval)
print("This is prev_data: ", prev_data)
# check each value in linked list against prev_data as long as value is not empty
while thisval is not None:
print("thisval is NOT NONE")
print("in while loop, thisval = ", thisval)
print("in while loop, prev_data = ", prev_data)
# if value is equal to prev_data
if thisval == prev_data:
print("thisval == prev_data")
# make the next of new_node the prev_data's next
new_node.nextNode = prev_data.nextNode
# make the next of prev_data the new_node
prev_data.nextNode = new_node
break;
# if value is not eqaul to prev_data then assign variable to next Node
else:
thisval = thisval.nextNode
def push_from_head(self, NewVal):
new_node = Node(NewVal)
print("This is new_node: ", new_node.data)
last = self.head
print("This is last/HEAD: ", last)
if self.head is None:
print("Head is NONE")
self.head = new_node
print("This is self.head: ",self.head)
return
print("last.nextNode: ", last.nextNode)
while last.nextNode is not None:
print("this is last inside while loop: ", last.data)
print("last.nextNode is not NONE")
last = last.nextNode
print("This is the last last: ", last.data)
last.nextNode = new_node
print("This is last.nextNode: ", last.nextNode)
def print_nodes(self):
if self.head:
thisval = self.head
while thisval:
print("This is node: ", thisval.data)
thisval = thisval.nextNode
e1 = LinkedList()
e1.push_from_head(10)
e1.push_from_head(20)
e1.push_from_head(30)
e1.push_from_head(40)
e1.push_from_head(50)
e1.insert_in_between(25, 20)
e1.print_nodes()
- Ok, so I want to insert the node (25) in between 20 and 30.
- In my method insert_in_between I'm taking two arguments: data and prev_data. Data is 25, but becomes a Node because I'm passing it into a Node class? But prev_data is an int(20).
- I was expecting this print statment to print
print("thisval == prev_data")whenthisval == prev_databut I think because there a mismatch between nodes and ints, that statment won't evaluate to true.
I'm sure this is an easy fix and have been trying to work out a solution with no luck. Can anyone point me in the right direction?
EDIT
When I change the line as suggested to: if thisval.data == prev_data: I get an error: AttributeError: 'int' object has no attribute 'nextNode' where it complains about this line: new_node.nextNode = prev_data.nextNode
回答1:
You are checking to see if an integer is equal to a node. That will never occur because they are different data types. You need to check
if thisval.data == prev_data
This will compare the data stored in each node object to the entered integer value (20) until it is found. The rest of your code should function correctly in this case.
回答2:
The above suggestion didn't quite work. I had to add a new method called getNodes() to get the index of the node so I can call it in my insert_in_between method.
class Node(object):
def __init__(self, data):
self.data = data
self.nextNode = None
class LinkedList(object):
def __init__(self):
self.head = None
self.tail = None
def getNode(self, index):
if self.head is not None:
current = self.head
count = 0
while(current):
if count == index:
return current;
else:
count+=1
current = current.nextNode
else:
print("There are no nodes")
# Insert inbetween
def insert_in_between(self, data, prev_data):
print("<<< INSERT INBETWEEN >>>")
# instantiate the new node
new_node = Node(data)
print("This is new_node: ", new_node)
# assign to head
thisval = self.head
print("This is thisval: ", thisval)
print("This is prev_data: ", prev_data)
prev_node = self.getNode(1)
print("This is prev_node: ", prev_node.data)
# check each value in linked list against prev_data as long as value is not empty
while thisval is not None:
print("thisval is NOT NONE")
print("in while loop, thisval = ", thisval)
print("in while loop, prev_data = ", prev_data)
# if value is equal to prev_node
if thisval.data == prev_node.data:
print("thisval == prev_node")
# make the next of new_node the prev_node's next
new_node.nextNode = prev_node.nextNode
# make the next of prev_node the new_node
prev_node.nextNode = new_node
break;
# if value is not eqaul to prev_data then assign variable to next Node
else:
thisval = thisval.nextNode
def push_from_head(self, NewVal):
new_node = Node(NewVal)
print("This is new_node: ", new_node.data)
last = self.head
print("This is last/HEAD: ", last)
if self.head is None:
print("Head is NONE")
self.head = new_node
print("This is self.head: ",self.head)
return
print("last.nextNode: ", last.nextNode)
while last.nextNode is not None:
print("this is last inside while loop: ", last.data)
print("last.nextNode is not NONE")
last = last.nextNode
print("This is the last last: ", last.data)
last.nextNode = new_node
print("This is last.nextNode: ", last.nextNode)
def print_nodes(self):
if self.head:
thisval = self.head
while thisval:
print("This is node: ", thisval.data)
thisval = thisval.nextNode
e1 = LinkedList()
e1.push_from_head(10)
e1.push_from_head(20)
e1.push_from_head(30)
e1.push_from_head(40)
e1.push_from_head(50)
e1.insert_in_between(25, 20)
e1.print_nodes()
来源：https://stackoverflow.com/questions/53346094/linkedlist-insert-between-nodes-not-inserting