Doubly Linked List (Answer)

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Link of DLL Chapter: DLL

Link of DLL Code Question: DLL Code Question

class Node:

    def __init__(self,prev=None,items=None,next=None):

        self.prev=prev

        self.items=items

        self.next=next

class DLL:

    def __init__(self,start=None):

        self.start=start

    def is_empty(self):

        return self.start==None

    def insert_at_start(self,data):

        n=Node(None,data,self.start)

        if not self.is_empty():

            self.start.prev=n

        self.start=n

    def insert_at_last(self,data):

        temp=self.start

        if self.start!=None:

            while temp.next!=None:

                temp=temp.next

        n=Node(temp,data,None)

        if temp==None:

            self.start=n

        else:

            temp.next=n

    def search(self,data):

        temp=self.start

        while temp!=None:

            if temp.items==data:

                return temp

            temp=temp.next

        return None

    def insert_after(self,temp,data):

        if temp!=None:

            n=Node(temp,data,temp.next)

            if temp.next!=None:

                temp.next.prev=n

            temp.next=n

    def print_list(self):

        temp=self.start

        while temp!=None:

            print(temp.items,end=" ")

            temp=temp.next

            print()

    def delete_first(self):

        if self.start is not None:

            self.start=self.start.next

            if self.start!=None:

                self.start.prev=None

    def delete_last(self):

        if self.start is None:

            pass

        elif self.start.next is None:

            self.start=None

        else:

            temp=self.start

            while temp.next is not None:

                temp=temp.next

            temp.prev.next=None

    def delete_item(self,data):

        if self.start is None:

            pass

        else:

            temp=self.start

            while temp is not None:

                if temp.items==data:

                    if temp.next is not None:

                        temp.next.prev=temp.prev

                    if temp.prev is not None:

                        temp.prev.next=temp.next

                    else:

                        self.start=temp.next

                    break

                temp=temp.next

    def __iter__(self):

        return DLLIterator(self.start)

class DLLIterator:

    def __init__(self,start):

        self.current=start

    def __iter__(self):

        return self

    def __next__(self):

        if not self.current:

            raise StopIteration

        data = self.current.items

        self.current=self.current.next

        return data

   

mylist=DLL()

mylist.insert_at_start(20)

mylist.insert_at_last(10)

mylist.insert_after(mylist.search(20),50)

for x in mylist:

    print(x,end=" ")

Tips to do Doubly Linked List:

Understand Nodes: Each node has data, prev (previous node), and next (next node).

Insertion: Add a new node by updating prev and next pointers of adjacent nodes and the new node.

Deletion: Remove a node by linking the prev of the next node and the next of the previous node to each other.

Traversal: Move through the list using next for forward traversal and prev for backward traversal.

Handle Edge Cases: Ensure proper handling when the list is empty or has only one node.