JAVA实现单链表和循环链表

定义接口

package DataStructure.linkedlist;

public interface List<E> {
    static final int ELEMENT_NOT_FOUND = -1;

    /**
     * 清除所有元素
     */
    void clear();

    /**
     * 元素的数量
     * @return
     */
    int size();

    /**
     * 是否为空
     * @return
     */
    boolean isEmpty();

    /**
     * 是否包含某个元素
     * @param element
     * @return
     */
    boolean contains(E element);

    /**
     * 添加到元素尾部
     * @param element
     */
    void add(E element);

    /**
     * 获取index位置的元素
     * @param index
     * @return
     */
    E get(int index);

    /**
     * 设置index位置的元素
     * @param index
     * @param element
     * @return
     */
    E set(int index, E element);

    /**
     * 在index位置插入一个元素
     * @param index
     * @param element
     */
    void add(int index, E element);

    /**
     * 删除index位置的元素
     * @param index
     * @return
     */
    E remove(int index);

    /**
     * 查看元素的索引
     * @param element
     * @return
     */
    int indexOf(E element);
}

定义抽象链表类

package DataStructure.linkedlist;

public abstract class AbstractList<E> implements List<E> {

    /**
     * 元素的数量
     */
    protected int size;

    /**
     * 元素的数量
     *
     * @return
     */
    @Override
    public int size() {
        return size;
    }

    /**
     * 是否为空
     *
     * @return
     */
    @Override
    public boolean isEmpty() {
        return size == 0;
    }

    /**
     * 是否包含某个元素
     *
     * @param element
     * @return
     */
    @Override
    public boolean contains(E element) {
        return indexOf(element) != ELEMENT_NOT_FOUND;
    }

    /**
     * 添加到元素尾部
     *
     * @param element
     */
    @Override
    public void add(E element) {
        add(size, element);
    }

    protected void outOfBounds(int index) {
        throw new IndexOutOfBoundsException("Index:" + index + ", Size:" + size);
    }

    protected void rangeCheck(int index) {
        if (index < 0 || index >= size) {
            outOfBounds(index);
        }
    }

    protected void rangeCheckForAdd(int index) {
        if (index < 0 || index > size) {
            outOfBounds(index);
        }
    }
}

实现单链表

package DataStructure.linkedlist;

public class SingleLinkedList<E> extends AbstractList<E> {
    private Node<E> first;

    public SingleLinkedList() {
        first = new Node<>(null, null);
    }

    private static class Node<E> {
        E element;
        Node<E> next;
        public Node(E element, Node<E> next) {
            this.element = element;
            this.next = next;
        }
    }

    /**
     * 清除所有元素
     */
    @Override
    public void clear() {
        size = 0;
        first = null;
    }

    /**
     * 获取index位置的元素
     *
     * @param index
     * @return
     */
    @Override
    public E get(int index) {
        return node(index).element;
    }

    /**
     * 设置index位置的元素
     *
     * @param index
     * @param element
     * @return
     */
    @Override
    public E set(int index, E element) {
        Node<E> node = node(index);
        E old = node.element;
        node.element = element;
        return old;
    }

    /**
     * 在index位置插入一个元素
     *
     * @param index
     * @param element
     */
    @Override
    public void add(int index, E element) {
        rangeCheckForAdd(index);

        Node<E> prev = index == 0 ? first : node(index - 1);
        prev.next = new Node<>(element, prev.next);

        size++;
    }

    /**
     * 删除index位置的元素
     *
     * @param index
     * @return
     */
    @Override
    public E remove(int index) {
        rangeCheck(index);

        Node<E> prev = index == 0 ? first : node(index - 1);
        Node<E> node = prev.next;
        prev.next = node.next;

        size--;
        return node.element;
    }

    /**
     * 查看元素的索引
     *
     * @param element
     * @return
     */
    @Override
    public int indexOf(E element) {
        if (element == null) {
            Node<E> node = first;
            for (int i = 0; i < size; i++) {
                if (node.element == null) return i;
                node = node.next;
            }
        } else {
            Node<E> node = first;
            for (int i = 0; i < size; i++) {
                if (element.equals(node.element)) return i;
                node = node.next;
            }
        }
        return ELEMENT_NOT_FOUND;
    }

    /**
     * 获取index位置对应的节点对象
     * @param index
     * @return
     */
    private Node<E> node(int index) {
        rangeCheck(index);

        Node<E> node = first.next;
        for (int i = 0; i < index; i++) {
            node = node.next;
        }
        return node;
    }

    @Override
    public String toString() {
        StringBuilder string = new StringBuilder();
        string.append("size=").append(size).append(", [");
        Node<E> node = first.next;
        for (int i = 0; i < size; i++) {
            if (i != 0) {
                string.append(", ");
            }
            string.append(node.element);
            node = node.next;
        }
        string.append("]");

        return string.toString();
    }
}

实现循环链表

package DataStructure.linkedlist;


public class CircleLinkedList<E> extends AbstractList<E> {

    private Node<E> first;
    private Node<E> last;
    private Node<E> current;

    private static class Node<E> {
        E element;
        Node<E> prev;
        Node<E> next;
        public Node(Node<E> prev, E element, Node<E> next) {
            this.prev = prev;
            this.element = element;
            this.next = next;
        }

        @Override
        public String toString() {
            StringBuilder sb = new StringBuilder();

            if (prev != null) {
                sb.append(prev.element);
            } else {
                sb.append("null");
            }

            sb.append("_").append(element).append("_");

            if (next != null) {
                sb.append(next.element);
            } else {
                sb.append("null");
            }

            return sb.toString();
        }
    }

    public void reset() {
        current = first;
    }

    public E next() {
        if (current == null) return null;
        current = current.next;
        return current.element;
    }

    public E remove() {
        if (current == null) return null;

        Node<E> next = current.next;
        E element = remove(current);
        if (size == 0) {
            current = null;
        } else {
            current = next;
        }
        return element;
    }

    @Override
    public void clear() {
        size = 0;
        first = null;
        last = null;
    }

    @Override
    public E get(int index) {
        return node(index).element;
    }

    @Override
    public E set(int index, E element) {
        Node<E> node = node(index);
        E old = node.element;
        node.element = element;
        return old;
    }

    @Override
    public void add(int index, E element) {
        rangeCheckForAdd(index);

        //(size == 0 && index == 0) 或者 向末尾添加元素
        if (size == index) {
            Node<E> oldLast = last;
            Node<E> last = new Node(oldLast, element, first);
            if (oldLast == null) { // 这是链表添加到第一个元素
                first = last;
                first.prev = first;
                first.next = first;
            } else {
                oldLast.next = last;
                first.prev = last;
            }
        } else {
            Node<E> next = node(index);
            Node<E> prev = next.prev;
            Node<E> node = new Node(prev, element, next);
            next.prev = node;
            prev.next = node;
            if (index == 0) {
                first = node;
            }
        }

        size++;
    }

    @Override
    public E remove(int index) {
        rangeCheck(index);

        return remove(node(index));
    }

    private E remove(Node<E> node) {
        if (size == 1) {
            first = null;
            last = null;
        } else {
            Node<E> prev = node.prev;
            Node<E> next = node.next;
            prev.next = next;
            next.prev = prev;

            if (node == first) {
                first = next;
            }

            if (node == last) {
                last = prev;
            }
        }

        size--;
        return node.element;
    }

    @Override
    public int indexOf(E element) {
        Node<E> node = first;
        if (element == null) {
            for (int i = 0; i < size; i++) {
                if (node.element == null) return i;
                node = node.next;
            }
        } else {
            for (int i = 0; i < size; i++) {
                if (element.equals(node.element)) return i;
                node = node.next;
            }
        }
        return ELEMENT_NOT_FOUND;
    }

    /**
     * 获取index位置对应节点的元素
     * @param index
     * @return
     */
    private Node<E> node(int index) {
        rangeCheck(index);

        if (index < (size >> 1)) {
            Node<E> node = first;
            for (int i = 0; i < index; i++) {
                node = node.next;
            }
            return node;
        } else {
            Node<E> node = last;
            for (int i = size - 1; i > index; i--) {
                node = node.prev;
            }
            return node;
        }
    }

    @Override
    public String toString() {
        StringBuilder string = new StringBuilder();
        string.append("size=").append(size).append(", [");
        Node<E> node = first;
        for (int i = 0; i < size; i++) {
            if (i != 0) {
                string.append(", ");
            }

            string.append(node);

            node = node.next;
        }
        string.append("]");
        return string.toString();
    }
}