9.2 KiB
Linked List Data Structure
Link list is a linear data Structure which can be defined as collection of objects called nodes that are randomly stored in the memory. A node contains two types of metadata i.e. data stored at that particular address and the pointer which contains the address of the next node in the memory.
The last element in a linked list features a null pointer.
Why use linked list over array?
From the beginning, we are using array data structure to organize the group of elements that are stored individually in the memory. However, there are some advantage and disadvantage of array which should be known to decide which data structure will used throughout the program.
limitations
- Before an array can be utilized in a program, its size must be established in advance.
- Expanding an array's size is a lengthy process and is almost impossible to achieve during runtime.
- Array elements must be stored in contiguous memory locations. To insert an element, all subsequent elements must be shifted
So we introduce a new data structure to overcome these limitations.
Linked list is used because,
- Dynamic Memory Management: Linked lists allocate memory dynamically, meaning nodes can be located anywhere in memory and are connected through pointers, rather than being stored contiguously.
- Adaptive Sizing: There is no need to predefine the size of a linked list. It can expand or contract during runtime, adapting to the program's requirements within the constraints of the available memory.
Let's code something
The smallest Unit: 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
Now, we will see the types of linked list.
There are mainly four types of linked list,
- Singly Link list
- Doubly link list
- Circular link list
- Doubly circular link list
1. Singly linked list.
Simply think it is a chain of nodes in which each node remember(contains) the addresses of it next node.
Creating a linked list class
class LinkedList:
def __init__(self):
self.head = None # Initialize head as None
Inserting a new node at the beginning of a linked list
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
Inserting a new node at the end of a linked list
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
Inserting a new node at the middle of a linked list
def insertAtPosition(self, data, position):
new_node = Node(data)
if position <= 0: #check if position is valid or not
print("Position should be greater than 0")
return
if position == 1:
new_node.next = self.head
self.head = new_node
return
current_node = self.head
current_position = 1
while current_node and current_position < position - 1: #Iterating to behind of the postion.
current_node = current_node.next
current_position += 1
if not current_node: #Check if Position is out of bound or not
print("Position is out of bounds")
return
new_node.next = current_node.next #connect the intermediate node
current_node.next = new_node
Printing the Linked list
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
Lets complete the code and create a linked list.
Connect all the code.
if __name__ == '__main__':
llist = LinkedList()
# Insert words at the beginning
llist.insertAtBeginning(4) # <4>
llist.insertAtBeginning(3) # <3> 4
llist.insertAtBeginning(2) # <2> 3 4
llist.insertAtBeginning(1) # <1> 2 3 4
# Insert a word at the end
llist.insertAtEnd(10) # 1 2 3 4 <10>
llist.insertAtEnd(7) # 1 2 3 4 10 <7>
#Insert at a random position
llist.insertAtPosition(9,4) ## 1 2 3 <9> 4 10 7
# Print the list
llist.printList()
output:
1 2 3 9 4 10 7
Deleting a node from the beginning of a linked list
check the list is empty otherwise shift the head to next 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
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
Search in a linked list
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"
if __name__ == '__main__':
llist = LinkedList()
# Insert words at the beginning
llist.insertAtBeginning(4) # <4>
llist.insertAtBeginning(3) # <3> 4
llist.insertAtBeginning(2) # <2> 3 4
llist.insertAtBeginning(1) # <1> 2 3 4
# Insert a word at the end
llist.insertAtEnd(10) # 1 2 3 4 <10>
llist.insertAtEnd(7) # 1 2 3 4 10 <7>
#Insert at a random position
llist.insertAtPosition(9,4) # 1 2 3 <9> 4 10 7
llist.insertAtPositon(56,4) # 1 2 3 <56> 9 4 10 7
#delete at the beginning
llist.deleteFromBeginning() # 2 3 56 9 4 10 7
#delete at the end
llist.deleteFromEnd() # 2 3 56 9 4 10
# Print the list
llist.printList()
Output:
2 3 56 9 4 10
Real Life uses of Linked List
Here are a few practical applications of linked lists in various fields:
-
Music Player: In a music player, songs are often linked to the previous and next tracks. This allows for seamless navigation between songs, enabling you to play tracks either from the beginning or the end of the playlist. This is akin to a doubly linked list where each song node points to both the previous and the next song, enhancing the flexibility of song selection.
-
GPS Navigation Systems: Linked lists can be highly effective for managing lists of locations and routes in GPS navigation systems. Each location or waypoint can be represented as a node, making it easy to add or remove destinations and to navigate smoothly from one location to another. This is similar to how you might plan a road trip, plotting stops along the way in a flexible, dynamic manner.
-
Task Scheduling: Operating systems utilize linked lists to manage task scheduling. Each process waiting to be executed is represented as a node in a linked list. This organization allows the system to efficiently keep track of which processes need to be run, enabling fair and systematic scheduling of tasks. Think of it like a to-do list where each task is a node, and the system executes tasks in a structured order.
-
Speech Recognition: Speech recognition software uses linked lists to represent possible phonetic pronunciations of words. Each potential pronunciation is a node, allowing the software to dynamically explore different pronunciation paths as it processes spoken input. This method helps in accurately recognizing and understanding speech by considering multiple possibilities in a flexible manner, much like evaluating various potential meanings in a conversation.
These examples illustrate how linked lists provide a flexible, dynamic data structure that can be adapted to a wide range of practical applications, making them a valuable tool in both software development and real-world problem-solving.