数据结构-队列-Java实现

数据结构-队列-Java实现

队列：先进先出

实现：链表形式

import java.util.Iterator;

/**
 * 队列
 */
public class Queue<T> implements Iterable<T>{

    private Node<T> head;//队头
    private int N;//对列内结点个数
    private Node<T> last;//队尾

    //初始化队列
    public Queue() {
        this.head = new Node<>(null, null);
        this.last = null;
        this.N = 0;
    }

    //判断队空
    public boolean isEmpty() {
        return N == 0;
    }

    public int size() {
        return N;
    }

    //出队
    public T dequeue() {
        if (isEmpty()) {
            throw new RuntimeException("队列为空，无法出队");
        }
        Node<T> result = head.next;
        head.next = head.next.next;
        N--;
        if (isEmpty()) {
            last = null;
        }
        return result.item;
    }

    //入队
    public void enqueue(T t) {
        if (last == null) {
            //当前队列为空，插入第一个结点，此时head.next 和 last 都指向第一个结点;
            last = new Node<>(t, null);
            head.next = last;
        } else {
            //队列不为空，此时需要将原最后一个结点的next = 新节点。且last = 新节点
            Node oldLast = last;
            last = new Node<>(t, null);
            oldLast.next = last;
        }
        N++;
    }

    @Override
    public Iterator<T> iterator() {
        return new SIterator<>();
    }

    private class SIterator<T> implements Iterator<T>{

        Node shead = head;

        @Override
        public boolean hasNext() {
            return shead.next != null;
        }

        @Override
        public T next() {
            Node<T> node = shead.next;
            shead = shead.next;
            return node.item;
        }
    }
    private class Node<T> {
        T item;
        Node<T> next;

        public Node(T item, Node<T> node) {
            this.item = item;
            this.next = node;
        }
    }
}

易忘点：在Iterator中next方法中，不要忘记进行结点的后移。