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Linked Lists in Python

Initializing a Node

class Node:
    def __init__(self, data):
        self.data = data  # Assigns the given data to the node
        self.next = None  # Initialize the next attribute to null

Inserting a New Node at the Beginning of a Linked List

class LinkedList:
    def __init__(self):
        self.head = None  # Initialize head as None
        
    def insertAtBeginning(self, new_data):
        new_node = Node(new_data)  # Create a new node 
        new_node.next = self.head  # Next for new node becomes the current head
        self.head = new_node  # Head now points to the new node

    def printList(self):
        temp = self.head # Start from the head of the list
        while temp:
            print(temp.data,end=' ') # Print the data in the current node
            temp = temp.next # Move to the next node
        print()  # Ensures the output is followed by a new line
if __name__ == '__main__':
    # Create a new LinkedList instance
    llist = LinkedList()

    # Insert each letter at the beginning using the method we created
    llist.insertAtBeginning('fox') 
    llist.insertAtBeginning('brown') 
    llist.insertAtBeginning('quick')  
    llist.insertAtBeginning('the')  

    # Now 'the' is the head of the list, followed by 'quick', then 'brown' and 'fox'

    # Print the list
    llist.printList()

Inserting a New Node at the End of a Linked List

class LinkedList:
    def __init__(self):
        self.head = None  # Initialize head as None
        
    def insertAtBeginning(self, new_data):
        new_node = Node(new_data)  # Create a new node 
        new_node.next = self.head  # Next for new node becomes the current head
        self.head = new_node  # Head now points to the new node

    def printList(self):
        temp = self.head # Start from the head of the list
        while temp:
            print(temp.data,end=' ') # Print the data in the current node
            temp = temp.next # Move to the next node
        print()  # Ensures the output is followed by a new line
        
    def insertAtEnd(self, new_data):
        new_node = Node(new_data)  # Create a new node
        if self.head is None:
            self.head = new_node  # If the list is empty, make the new node the head
            return
        last = self.head 
        while last.next:  # Otherwise, traverse the list to find the last node
            last = last.next
        last.next = new_node  # Make the new node the next node of the last node
if __name__ == '__main__':
    llist = LinkedList()

    # Insert words at the beginning
    llist.insertAtBeginning('fox')
    llist.insertAtBeginning('brown')
    llist.insertAtBeginning('quick')
    llist.insertAtBeginning('the')

    # Insert a word at the end
    llist.insertAtEnd('jumps')

    # Print the list
    llist.printList()

Deleting a Node from the Beginning of a Linked List

class LinkedList:
    def __init__(self):
        self.head = None  # Initialize head as None
        
    def insertAtBeginning(self, new_data):
        new_node = Node(new_data)  # Create a new node 
        new_node.next = self.head  # Next for new node becomes the current head
        self.head = new_node  # Head now points to the new node

    def printList(self):
        temp = self.head # Start from the head of the list
        while temp:
            print(temp.data,end=' ') # Print the data in the current node
            temp = temp.next # Move to the next node
        print()  # Ensures the output is followed by a new line
        
    def insertAtEnd(self, new_data):
        new_node = Node(new_data)  # Create a new node
        if self.head is None:
            self.head = new_node  # If the list is empty, make the new node the head
            return
        last = self.head 
        while last.next:  # Otherwise, traverse the list to find the last node
            last = last.next
        last.next = new_node  # Make the new node the next node of the last node
        
    def deleteFromBeginning(self):
        if self.head is None:
            return "The list is empty" # If the list is empty, return this string
        self.head = self.head.next  # Otherwise, remove the head by making the next node the new head

Deleting a Node from the End of a Linked List

class LinkedList:
    def __init__(self):
        self.head = None  # Initialize head as None
        
    def insertAtBeginning(self, new_data):
        new_node = Node(new_data)  # Create a new node 
        new_node.next = self.head  # Next for new node becomes the current head
        self.head = new_node  # Head now points to the new node

    def printList(self):
        temp = self.head # Start from the head of the list
        while temp:
            print(temp.data,end=' ') # Print the data in the current node
            temp = temp.next # Move to the next node
        print()  # Ensures the output is followed by a new line
        
    def insertAtEnd(self, new_data):
        new_node = Node(new_data)  # Create a new node
        if self.head is None:
            self.head = new_node  # If the list is empty, make the new node the head
            return
        last = self.head 
        while last.next:  # Otherwise, traverse the list to find the last node
            last = last.next
        last.next = new_node  # Make the new node the next node of the last node
        
    def deleteFromBeginning(self):
        if self.head is None:
            return "The list is empty" # If the list is empty, return this string
        self.head = self.head.next  # Otherwise, remove the head by making the next node the new head
        
    def deleteFromEnd(self):
        if self.head is None:
            return "The list is empty" 
        if self.head.next is None:
            self.head = None  # If there's only one node, remove the head by making it None
            return
        temp = self.head
        while temp.next.next:  # Otherwise, go to the second-last node
            temp = temp.next
        temp.next = None  # Remove the last node by setting the next pointer of the second-last node to None
if __name__ == '__main__':
    llist = LinkedList()

    # Insert words at the beginning
    llist.insertAtBeginning('fox')
    llist.insertAtBeginning('brown')
    llist.insertAtBeginning('quick')
    llist.insertAtBeginning('the')

    # Insert a word at the end
    llist.insertAtEnd('jumps')

   # Print the list before deletion
    print("List before deletion:")
    llist.printList()

    # Deleting nodes from beginning and end
    llist.deleteFromBeginning()
    llist.deleteFromEnd()

    # Print the list after deletion
    print("List after deletion:")
    llist.printList()

Searching the Linked List for a Specific Value

class LinkedList:
    def __init__(self):
        self.head = None  # Initialize head as None
        
    def insertAtBeginning(self, new_data):
        new_node = Node(new_data)  # Create a new node 
        new_node.next = self.head  # Next for new node becomes the current head
        self.head = new_node  # Head now points to the new node

    def printList(self):
        temp = self.head # Start from the head of the list
        while temp:
            print(temp.data,end=' ') # Print the data in the current node
            temp = temp.next # Move to the next node
        print()  # Ensures the output is followed by a new line
        
    def insertAtEnd(self, new_data):
        new_node = Node(new_data)  # Create a new node
        if self.head is None:
            self.head = new_node  # If the list is empty, make the new node the head
            return
        last = self.head 
        while last.next:  # Otherwise, traverse the list to find the last node
            last = last.next
        last.next = new_node  # Make the new node the next node of the last node
        
    def deleteFromBeginning(self):
        if self.head is None:
            return "The list is empty" # If the list is empty, return this string
        self.head = self.head.next  # Otherwise, remove the head by making the next node the new head
        
    def deleteFromEnd(self):
        if self.head is None:
            return "The list is empty" 
        if self.head.next is None:
            self.head = None  # If there's only one node, remove the head by making it None
            return
        temp = self.head
        while temp.next.next:  # Otherwise, go to the second-last node
            temp = temp.next
        temp.next = None  # Remove the last node by setting the next pointer of the second-last node to None
        
    def search(self, value):
        current = self.head  # Start with the head of the list
        position = 0  # Counter to keep track of the position
        while current: # Traverse the list
            if current.data == value: # Compare the list's data to the search value
                return f"Value '{value}' found at position {position}" # Print the value if a match is found
            current = current.next
            position += 1
        return f"Value '{value}' not found in the list"
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