Course Content
Algorithms and Data Structures Overview
Algorithms and Data Structures Overview
Doubly Linked List
The linked list is a versatile data structure, free from the "holes" inherent in arrays.
Manipulating the first element is efficient, but for certain abstract data types like queues, efficient manipulation of the last element and bidirectional traversal are needed. Standard linked lists struggle with accessing the last element, requiring O(N) time complexity.
Doubly linked lists resolve this limitation and offer solutions to various other challenges.
from lolviz import * from IPython.display import display_png class Node: def __init__(self, data): self.value = data self.next = None self.previous = None # Let's create some nodes node1 = Node(1) node2 = Node(2) node3 = Node(3) # Then let's couple them into a linked list node1.next = node2 node2.next = node3 # And don't forget to assign the reference to a previous node node2.previous = node1 node3.previous = node2 display_png(objviz(node1))
The doubly linked list's nodes contain the references to the next and to the previous elements. Therefore we can access the first and the last item in O(1) constant running time. Time complexity of all other operations for doubly linked list is the same as for the simple linked list.
def search(self, value):
# Start the search from the head of the linked list
current = self.head
# Traverse the linked list
while current:
# Check if the value of the current node matches the target value
if current.data == value:
# Return the node if found
return current
# Move to the next node
current = current.next
# Return None if the value is not found in the linked list
return None
def insert(self, value):
# Create a new node with the given value
new_node = ListNode(value)
# Check if the linked list is empty
if not self.head:
# If the linked list is empty, set the new node as the head
self.head = new_node
else:
# If the linked list is not empty, insert the new node at the beginning
new_node.next = self.head
self.head.prev = new_node
self.head = new_node
def delete(self, value):
# Start the search from the head of the linked list
current = self.head
# Traverse the linked list
while current:
# Check if the value of the current node matches the target value
if current.data == value:
# Update the pointers of the surrounding nodes to skip the current node
if current.prev:
current.prev.next = current.next
if current.next:
current.next.prev = current.prev
# Update the head pointer if the current node is the head
if current == self.head:
self.head = current.next
# Exit the method after deleting the node
return
# Move to the next node
current = current.next
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