Algorithms4th/src/ch1/sec3/LinkQueue.java

package ch1.sec3;

import java.util.Iterator;

public class LinkQueue<Item> implements Iterable<Item> {
    private Node head;
    private Node tail;
    private int size;

    @Override
    public LinkQueueIterator iterator() {
        return new LinkQueueIterator();
    }

    public LinkQueue() {
        head = null;
        tail = null;
        size = 0;
    }

    public void enqueue(Item item) {
        if (isEmpty()) {
            head = new Node(item, null);
            tail = head;
        } else {
            tail.next = new Node(item, null);
            tail = tail.next;
        }
        size++;
    }

    public Item dequeue() {
        if (isEmpty()) {
            return null;
        }
        Item item = head.value;
        head = head.next;
        if (size() == 1) {
            tail = tail.next;
        }
        size--;
        return item;
    }

    public boolean isEmpty() {
        return size == 0;
    }

    public int size() {
        return size;
    }

    public static void main(String[] args) {
        LinkQueue<Integer> linkQueue = new LinkQueue<>();
        System.out.println(linkQueue.isEmpty());
        linkQueue.enqueue(1);
        linkQueue.enqueue(2);
        linkQueue.enqueue(3);
        for (Integer i : linkQueue) {
            System.out.println(i);
        }
        System.out.println(linkQueue.size());
        while (!linkQueue.isEmpty()) {
            System.out.println(linkQueue.dequeue());
        }
    }

    private class Node {
        private Item value;
        private Node next;
        public Node(Item value, Node next) {
            this.value = value;
            this.next = next;
        }
    }

    private class LinkQueueIterator implements Iterator<Item> {
        private Node current;

        public LinkQueueIterator() {
            current = head;
        }

        @Override
        public boolean hasNext() {
            return current != null;
        }

        @Override
        public Item next() {
            Item item = current.value;
            current = current.next;
            return item;
        }
    }
}