/**
* Program Title: Queue (Linked List Implementation)
* Author: [Ahad-23]
* Date: 2025-10-08
*
* Description: Implements a generic Queue data structure using a custom
* Singly Linked List. Operations (enqueue, dequeue, peek) are designed
* to adhere to the FIFO (First-In, First-Out) principle.
*
* Time Complexity: O(1) for all main operations (enqueue, dequeue, peek).
* Space Complexity: O(N) where N is the number of elements stored.
*/
public class Queue {
// Node class for custom singly linked list
private static class Node {
T data;
Node next;
Node(T data) {
this.data = data;
this.next = null;
}
}
private Node front;
private Node rear;
private int size;
public Queue() {
this.front = null;
this.rear = null;
this.size = 0;
}
public void enqueue(T data) {
Node newNode = new Node<>(data);
if (rear == null) front = rear = newNode;
else
{
rear.next = newNode;
rear = newNode;
}
size++;
}
public T dequeue() {
if (isEmpty()) {
throw new NoSuchElementException("Queue is empty. Cannot dequeue.");
}
T value = front.data;
front = front.next;
if (front == null) rear = null;
size--;
return value;
}
public T peek() {
if (isEmpty()) {
throw new NoSuchElementException("Queue is empty. Cannot dequeue.");
}
return front.data;
}
public boolean isEmpty() {
return front == null;
}
// Get current size of the queue
public int size() {
return size;
}
}