双向链表实现栈和队列

/**
 * 双向链表实现栈和队列
 */
public class DoubleEndsNodeToQueueAndStack {

    public static class MyQueue<T> {

        public DoubleEndsNode<T> nodes;

        public MyQueue() {
            nodes = new DoubleEndsNode();
        }

        public void push(T value) {
            nodes.addFromHead(value);
        }

        public T poll() {
            return nodes.popFromBottom();
        }

        public boolean isEmpty() {
            return nodes.isEmpty();
        }

    }

    public static class MyStack<T> {

        public DoubleEndsNode<T> nodes;

        public MyStack() {
            nodes = new DoubleEndsNode();
        }

        public void push(T value) {
            nodes.addFromHead(value);
        }

        public T pop() {
            return nodes.popFromHead();
        }

        public boolean isEmpty() {
            return nodes.isEmpty();
        }

    }

    public static class DoubleEndsNode<T> {

        public Node<T> head;

        public Node<T> tail;

        public void addFromHead(T value) {
            Node node = new Node(value);
            if (head == null) {
                head = node;
                tail = node;
            } else {
                node.next = head;
                head.pre = node;
                head = node;
            }
        }

        public void addFromBottom(T value) {
            Node node = new Node(value);
            if (head == null) {
                head = node;
                tail = node;
            } else {
                tail.next = node;
                node.pre = tail;
                tail = node;
            }
        }

        public T popFromHead() {
            if (head == null) {
                return null;
            }
            Node<T> node = head;
            if (head == tail) {
                head = null;
                tail = null;
            } else {
                head = head.next;
                head.pre = null;
                node.next = null;
            }
            return node.value;
        }

        public T popFromBottom() {
            if (head == null) {
                return null;
            }
            Node<T> node = tail;
            if (head == tail) {
                head = null;
                tail = null;
            } else {
                tail = tail.pre;
                tail.next = null;
                node.pre = null;
            }
            return node.value;
        }

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

    }

    public static class Node<T> {

        public T value;

        public Node<T> pre;

        public Node<T> next;

        public Node(T node) {
            this.value = node;
        }

    }

}

/* 如有错误，欢迎批评指正 */