Queue Using Linked List - Coursera Algorithms

Queues follow FIFO standard. To implement, we need to maintain two pointers to first and last nodes of linked list, as we insert at the end of the list and removed the first element of the list for enqueue and dequeue operations.

Following is the program:

	package queues;
	public class QueueLL {
	Node first;
	Node last;
	static int size;
	public class Node{
	String value;
	Node next;
	public Node(String s) {
	this.value = s;
	}
	}
	public void enqueue(String s) {
	Node prevLast = last;
	last = new Node(s);
	if(!isEmpty())
	prevLast.next = last;
	else {
	first = last;
	}
	size++;
	}
	public String dequeue() {
	if(isEmpty()) {
	System.out.println("queue empty");
	return "";
	}
	String s = first.value;
	first = first.next;
	size--;
	return s;
	}
	public boolean isEmpty() {
	return (first==null);
	}
	public int size() {
	return size;
	}
	public void print() {
	System.out.println("==========================");
	Node n = first;
	while(n!=null) {
	System.out.println(n.value);
	n = n.next;
	}
	}
	public static void main(String[] args) {
	QueueLL queue = new QueueLL();
	queue.enqueue("to");
	queue.enqueue("be");
	queue.enqueue("or");
	queue.enqueue("not");
	queue.enqueue("to");
	queue.enqueue("be");
	queue.print();
	System.out.println("DQd "+queue.dequeue());
	System.out.println("DQd "+queue.dequeue());
	System.out.println("DQd "+queue.dequeue());
	System.out.println("DQd "+queue.dequeue());
	System.out.println("DQd "+queue.dequeue());
	System.out.println("DQd "+queue.dequeue());
	System.out.println("DQd "+queue.dequeue());
	queue.print();
	}
	}

view raw QueueLL.java hosted with ❤ by GitHub