數據結構---雙向鏈表

1. 概述

1. 雙向鏈表：每一個節點存在前項指針和後項指針，方便對於節點的操做。不須要，考慮如何獲取前項節點而苦惱。

2. 源碼

/** * 雙向鏈表: 存在前項指針和後項指針 * @param <T> */
public class TwoWayList<T> {
    public class Node {
        public T data;
        private Node next, prev;

        public Node(T e, Node next) {
            this.data = e;
            this.next = next;
        }

        public Node(T e) {
            this(e, null);
        }

        public Node() {
            this(null, null);
        }

        @Override
        public String toString() {
            return data.toString();
        }
    }

    private Node head, tail;

    private int size;

    public int getSize() {
        return size;
    }

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

    public void add(T e) {
        if (tail == null) {
            tail = new Node(e);
            head = tail;
        } else {
            Node newNode = new Node(e);
            newNode.prev = tail;
            tail.next = newNode;
            tail = newNode;
        }

        size++;
    }

    public void addFirst(T e) {
        if (tail == null) {
            tail = new Node(e);
            head = tail;
        } else {
            Node newNode = new Node(e);
            head.prev = newNode;
            newNode.next = head;
            head = newNode;
        }

        size++;
    }

    public void addLast(T e) {
        add(e);
    }

    public T removeFirst() {
        if (tail == null) {
            throw new IllegalArgumentException("List is empty!");
        }

        Node cur = head;
        head = head.next;
        cur.next = null;
        size--;

        return cur.data;
    }

    public T removeLast() {
        if (tail == null) {
            throw new IllegalArgumentException("List is empty!");
        }

        Node cur = tail;
        tail = tail.prev;
        tail.next = null;
        cur.prev = null;
        size--;

        return cur.data;
    }

    public T getFirst() {
        if (tail == null) {
            throw new IllegalArgumentException("List is empty!");
        }

        return head.data;
    }

    public T getLast() {
        if (tail == null) {
            throw new IllegalArgumentException("List is empty!");
        }

        return tail.data;
    }

    @Override
    public String toString() {
        StringBuilder result = new StringBuilder();
        Node cur = head;
        while (cur != null) {
            result.append(cur + "->");
            cur = cur.next;
        }

        result.append("Null");
        return result.toString();
    }

    public static void main(String[] args) {
        TwoWayList<Integer> list = new TwoWayList<>();
        IntStream.range(0, 10).forEach(item -> {
            list.addFirst(item);
            System.out.println(list);
        });

        System.out.println("==========DEL First==========");
        IntStream.range(0, 3).forEach(item -> {
            list.removeFirst();
            System.out.println(list);
        });

        System.out.println("==========DEL Last==========");
        IntStream.range(0, 3).forEach(item -> {
            list.removeLast();
            System.out.println(list);
        });

        System.out.println("==========GET First&Last==========");
        System.out.println(list.getFirst());
        System.out.println(list.getLast());
    }
}