算法4学习-1.3.3.9 Queue链表实现

继续上一节,队列的实现，背包差不多就不写出来了。

代码

import java.util.Iterator;

/**
 * FIFO队列 Created by tuzhis on 2016年1月15日.
 */
public class Queue<Item> implements Iterable<Item> {
    private Node first; // 指向最早添加的节点的链接
    private Node last;  // 指向最近添加的节点的链接
    private int N;      // 队列中的元素个数

    private class Node {
        Item item;
        Node next;
    }

    public boolean isEmpty() {
        return first == null;
    }

    public int size() {
        return N;
    }

    public void enqueue(Item item) {
        Node oldNode = last;
        last.item = item;
        last.next = null;
        if (isEmpty())
            first = last;
        else
            oldNode.next = last;
        N++;
    }

    public Item dequeue() {
        Item item = first.item;
        first = first.next;
        if (isEmpty())
            last = null;
        N--;
        return item;
    }

    @Override
    public Iterator<Item> iterator() {
        return new ListIterator();
    }

    private class ListIterator implements Iterator<Item> {
        private Node current = first;

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

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

    }
}

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