数据结构 Linked List 实现和使用。

LinkedList 类

public class LinkedList<E> {

    private class Node {
        public E e;
        public Node next;

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

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

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

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

    private Node dummyHead;
    private int size;

    public LinkedList() {
        dummyHead = new Node(null, null);
        size = 0;
    }

    // 获取链表中元素个数
    public int getSize() {
        return size;
    }

    // 返回链表是否为空
    public boolean isEmpty() {
        return size == 0;
    }

    // 在链表的index(0-based)位置添加新元素 e
    public void add(int index, E e) {

        if (index < 0 || index > size) {
            throw new IllegalArgumentException("Add failed. Illegal index.");
        }

        Node prev = dummyHead;
        for (int i = 0; i < index; i++) {
            prev = prev.next;
        }

//      Node node = new Node(e);
//      node.next = prev.next;
//      prev.next = node;

        prev.next = new Node(e, prev.next);
        size ++;
    }

    // 在链表头添加新元素 e
    public void addFirst(E e) { add(0, e); }

    // 在链表末尾添加元素 e
    public void addLast(E e) {
        add(size, e);
    }

    // 获得链表的第 index(0-based) 个位置的元素
    public E get(int index) {

        if (index < 0 || index >= size) {
            throw new IllegalArgumentException("Get failed.Illegal index.");
        }

        Node cur = dummyHead.next;
        for(int i = 0; i < index; i++) {
            cur = cur.next;
        }
        return cur.e;
    }

    // 获得链表的第一个元素
    public E getFirst() { return get(0); }

    // 获得链表的最后一个元素
    public E getLast() { return get(size - 1); }

    // 修改链表的第 index(0-based) 个位置的元素为 e
    public void set(int index, E e) {

        if (index < 0 || index >= size) {
            throw new IllegalArgumentException("Get failed.Illegal index.");
        }

        Node cur = dummyHead.next;
        for (int i = 0; i < index; i++) {
            cur = cur.next;
        }
        cur.e = e;
    }

    // 查找链表中是否存在元素 e
    public boolean contains(E e) {

        Node cur = dummyHead.next;
        while (cur != null) {
            if (cur.e.equals(e)) {
                return true;
            }
            cur = cur.next;
        }
        return false;
    }

    // 从链表中删除 index(0-based) 位置的元素,返回删除的元素
    public E remove(int index) {

        if (index < 0 || index >= size) {
            throw new IllegalArgumentException("Get failed.Illegal index.");
        }

        Node prev = dummyHead;
        for (int i = 0; i < index; i++) {
            prev = prev.next;
        }

        Node retNode = prev.next;
        prev.next = retNode.next;
        retNode.next = null;
        size--;

        return retNode.e;
    }

    // 从链表中删除第一个元素,返回删除的元素
    public E removeFirst() {
        return remove(0);
    }

    // 从链表中删除最后一个元素,返回删除的元素
    public E removeLast() {
        return remove(size - 1);
    }

    @Override
    public String toString() {

        StringBuilder res = new StringBuilder();

        Node cur = dummyHead.next;
        while (cur != null) {
            res.append(cur + "->");
            cur = cur.next;
        }
        res.append("NULL");

        return res.toString();
    }
}

LinkedList 类测试

public class Main {

    public static void main(String[] args) {

        LinkedList<Integer> linkedList = new LinkedList<>();
        for(int i = 0; i < 5; i++) {
            linkedList.addFirst(i);
            System.out.println(linkedList);
        }

        linkedList.add(2, 666);
        System.out.println(linkedList);

        linkedList.remove(2);
        System.out.println(linkedList);

        linkedList.removeFirst();
        System.out.println(linkedList);

        linkedList.removeLast();
        System.out.println(linkedList);
    }
}

运行结果

0->NULL
1->0->NULL
2->1->0->NULL
3->2->1->0->NULL
4->3->2->1->0->NULL
4->3->666->2->1->0->NULL
4->3->2->1->0->NULL
3->2->1->0->NULL
3->2->1->NULL