When it is required to implement a queue data structure using a linked list, a method to add (enqueue operation) elements to the linked list, and a method to delete (dequeue operation) the elements of the linked list are defined.
Below is a demonstration for the same −
class Node: def __init__(self, data): self.data = data self.next = None class Queue_structure: def __init__(self): self.head = None self.last = None def enqueue_operation(self, data): if self.last is None: self.head = Node(data) self.last = self.head else: self.last.next = Node(data) self.last = self.last.next def dequeue_operation(self): if self.head is None: return None else: val_returned = self.head.data self.head = self.head.next return val_returned my_instance = Queue_structure() while True: print('enqueue <value>') print('dequeue') print('quit') my_input = input('What operation would you like to perform ? ').split() operation = my_input.strip().lower() if operation == 'enqueue': my_instance.enqueue_operation(int(my_input)) elif operation == 'dequeue': dequeued = my_instance.dequeue_operation() if dequeued is None: print('The queue is empty.') else: print('The deleted element is : ', int(dequeued)) elif operation == 'quit': break
enqueue <value> dequeue quit What operation would you like to perform ? enqueue 45 enqueue <value> dequeue quit What operation would you like to perform ? enqueue 12 enqueue <value> dequeue quit What operation would you like to perform ? dequeue The deleted element is : 45 enqueue <value> dequeue quit What operation would you like to perform ? quit
The ‘Node’ class is created.
Another ‘Queue_structure’ class with required attributes is created.
It has an ‘init’ function that is used to initialize the first element, i.e the ‘head’ to ‘None’.
A method named enqueue_operation’ is defined, that helps add a value to the queue.
Another method named ‘dequeue_operation’ is defined, that helps delete a value from the queue, and returns the deleted value.
An instance of the ‘Queue_structure’ is created.
Three options are given, such as ‘enqueue’, ‘dequeue’, and ‘quit’.
The ‘enqueue’ option adds a specific value to the stack.
The ‘dequeue’ option deletes the element from the queue.
The ‘quit’ option comes out of the loop.
Based on the input/choice by user, the respective operations are performed.
This output is displayed on the console.