A

so the queue follows the

if we want to enter a new value then we use the rear end and if we want to delete the value then we use the front end.

to implement a queue using array first we need to choose the position of the front end rear end. we use the first index of array as the front end and last index as rear end.

In the above example first, we take an empty array and then we enqueue the values 20, 30, 15 and 40 and after that, we dequeue the value 20, 30 from the front end and then we again enqueue the value 56 and then dequeue the value 15.

to implement a queue using the linked list we first store the first node and last node's reference into the front end rear variables. because using the front variable we perform deletion in a queue and using the rear variable we perform insertion in a queue.

so the beginning of the list called the front end of the queue and end of the list called the rear end of the queue.

Deletion in the linked list

Insertion in the linked list

**queue**is an**abstract data structure**in which the**insertion**is performed on one end and**deletion**is performed on the other end.## Example of Queue in Data structures

In the above-given image, you see that the customers are standing in a line. and the customer who entered the line will go first means First in First out. and we can add the new customers in line at the end of the line and will go out from the beginning of the line.so the queue follows the

**FIFO**( First in First out ) process. and we can insert a new value from one end and delete the first inserted value from the other end.#### Enqueue operation

To insert a new value in the queue is called the Enqueue operation in the queue#### Dequeue operation

To delete the first entered value in the queue is called the Dequeue operation in the queue.#### Front end

the end from which we delete the value in the queue is called the Front end of the queue.#### Rear-end

the end from which we insert a new value in the queue is called the rear end of the queue.if we want to enter a new value then we use the rear end and if we want to delete the value then we use the front end.

### Implementation of the queue using the array.

to implement a queue using array first we need to choose the position of the front end rear end. we use the first index of array as the front end and last index as rear end.

In the above example first, we take an empty array and then we enqueue the values 20, 30, 15 and 40 and after that, we dequeue the value 20, 30 from the front end and then we again enqueue the value 56 and then dequeue the value 15.

#### Program to implement queue using array in a python programming language.

class EmptyQueueError(Exception): pass class Queue: def __init__(self): self.items = [] def is_empty(self): return self.items == [] def size(self): return len(self.items) def enqueue(self,item): self.items.append(item) def dequeue(self): if self.is_empty(): raise EmptyQueueError("Queue is Empty") return self.items.pop(0) def peek(self): if self.is_empty(): raise EmptyQueueError("Queue is Empty") return self.items[0] def display(self): print(self.items) ############## if __name__ == '__main__': qu = Queue() while True: print("1. Enqueue") print("2. Dequeue") print("3. Peek") print("4. Size") print("5. Display") print("6. Quit") choice = int(input("Enter your choice : ")) if choice == 1: x = int(input("Enter the element : ")) qu.enqueue(x) elif choice == 2: x=qu.dequeue() print("Element deleted fro the queue is : ", x) elif choice == 3: print("Element at the front end is ", qu.peek()) elif choice == 4: print("Size of queue ", qu.size()) elif choice == 5: qu.display() elif choice == 6: break else: print("Wrong choice ") print()

### Implementation of the queue using the linked list

to implement a queue using the linked list we first store the first node and last node's reference into the front end rear variables. because using the front variable we perform deletion in a queue and using the rear variable we perform insertion in a queue.

so the beginning of the list called the front end of the queue and end of the list called the rear end of the queue.

#### Dequeue operation

we already know how to delete the first node of the linked list and delete the node in the only linked list. and if you don't know then please go through this tutorialDeletion in the linked list

#### Enqueue operation

we already know how to insert a new node at the end of the linked list. and if you don't know then please go through this tutorialInsertion in the linked list

#### Program to implement the queue using the linked list in the python programming language.

class EmptyQueueError(Exception): pass class Node: def __init__(self, value): self.info = value self.link = None class Queue: def __init__(self): self.rear = None def is_empty(self): return self.rear is None def size(self): if self.is_empty(): return 0 n = 0 p = self.rear.link while True: n += 1 p = p.link if p == self.rear.link: break return n def enqueue(self, data): temp = Node(data) if self.is_empty(): self.rear = temp self.rear.link = self.rear else: temp.link = self.rear.link self.rear.link = temp self.rear = temp def dequeue(self): if self.is_empty(): raise EmptyQueueError("Queue is Empty ") if self.rear.link == self.rear: temp = self.rear self.rear = None else: temp = self.rear.link self.rear.link = self.rear.link.link return temp.info def peek(self): if self.is_empty(): raise EmptyQueueError("Queue is Empty") return self.rear.link.info def display(self): if self.is_empty(): print("List is empty") return p = self.rear.link while True: print(p.info, " ", end='') p = p.link if p == self.rear.link: break print() ##################### if __name__ == '__main__': qu = Queue() while True: print("1. Enqueue") print("2. Dequeue") print("3. Peek") print("4. Size") print("5. Display") print("6. Quit") choice = int(input("Enter your choice : ")) if choice == 1: x = int(input("Enter the element : ")) qu.enqueue(x) elif choice == 2: x = qu.dequeue() print("Element deleted from the queue is : ", x) elif choice == 3: print("Element at the front end is ", qu.peek()) elif choice == 4: print("Size of queue ", qu.size()) elif choice == 5: qu.display() elif choice == 6: break else: print("Wrong choice") print()

#### Also, read these posts

- What are Data Structures and algorithms
- Algorithm design and analysis
- Classification of algorithms
- How to calculate the running time of an algorithm.
- Worst Average and Best-case analysis of the algorithm.
- Big o notation
- Big o notation examples
- Linked List in Data Structures
- Traversing in Linked list
- Operations on the linked list
- Insertion in the linked list
- Deletion in a linked list
- Reversing a linked list
- Sorting a linked list
- Find and remove the loop in the linked list
- Doubly linked list
- Insertion in the doubly linked list
- Deletion in the doubly linked list
- Reversing a doubly linked list
- Circular linked list
- Insertion in the circular linked list
- Deletion in the circular linked list
- Merge two linked list
- Header linked list
- Sorted linked list
- Stack in data structures
- Circular queue
- Dequeue in the data structure
- Priority queue
- Polish notation
- Tree in the data structure
- Binary tree
- Array representation of the binary tree
- linked representation of a binary tree
- Traversing in the binary tree
- Inorder traversal in the binary tree
- Preorder traversal in the binary tree
- Postorder traversal in the binary tree
- Level order traversal in the binary tree
- Binary search tree
- Insertion in the binary search tree
- Deletion in the binary search tree
- Heap in data structures

- What are Data Structures and algorithms
- Algorithm design and analysis
- Classification of algorithms
- How to calculate the running time of an algorithm.
- Worst Average and Best-case analysis of the algorithm.
- Big o notation
- Big o notation examples
- Linked List in Data Structures
- Traversing in Linked list
- Operations on the linked list
- Insertion in the linked list
- Deletion in a linked list
- Reversing a linked list
- Sorting a linked list
- Find and remove the loop in the linked list
- Doubly linked list
- Insertion in the doubly linked list
- Deletion in the doubly linked list
- Reversing a doubly linked list
- Circular linked list
- Insertion in the circular linked list
- Deletion in the circular linked list
- Merge two linked list
- Header linked list
- Sorted linked list
- Stack in data structures
- Circular queue
- Dequeue in the data structure
- Priority queue
- Polish notation
- Tree in the data structure
- Binary tree
- Array representation of the binary tree
- linked representation of a binary tree
- Traversing in the binary tree
- Inorder traversal in the binary tree
- Preorder traversal in the binary tree
- Postorder traversal in the binary tree
- Level order traversal in the binary tree
- Binary search tree
- Insertion in the binary search tree
- Deletion in the binary search tree
- Heap in data structures

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