Java数据结构-03单链表（二）

在之前我们封装了一些操作在接口类中，并在抽象类实现了相同的方法。下面我们开始写代码：

无头结点单链表：(注意下面的AbstractList是之前抽取的类，不是java.util包下的类)

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

    private static class Node<E> {
        E element;
        Node<E> next;

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

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

    @Override
    public E get(int index) {
        /*
         * 最好：O(1)
         * 最坏：O(n)
         * 平均：O(n)
         */
        return node(index).element;
    }

    @Override
    public E set(int index, E element) {
        /*
         * 最好：O(1)
         * 最坏：O(n)
         * 平均：O(n)
         */
        Node<E> node = node(index);
        E old = node.element;
        node.element = element;
        return old;
    }

    @Override
    public void add(int index, E element) {
        /*
         * 最好：O(1)
         * 最坏：O(n)
         * 平均：O(n)
         */
        rangeCheckForAdd(index);

        if (index == 0) {
            first = new Node<>(element, first);
        } else {
            Node<E> prev = node(index - 1);
            prev.next = new Node<>(element, prev.next);
        }
        size++;
    }

    @Override
    public E remove(int index) {
        /*
         * 最好：O(1)
         * 最坏：O(n)
         * 平均：O(n)
         */
        rangeCheck(index);

        Node<E> node = first;
        if (index == 0) {
            first = first.next;
        } else {
            Node<E> prev = node(index - 1);
            node = prev.next;
            prev.next = node.next;
        }
        size--;
        return node.element;
    }

    @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;
        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;
        for (int i = 0; i < size; i++) {
            if (i != 0) {
                string.append(", ");
            }

            string.append(node.element);

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

有头结点的单链表

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;
        }
    }

    @Override
    public void clear() {
        size = 0;
        first = 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);
        
        Node<E> prev = index == 0 ? first : node(index - 1);
        prev.next = new Node<>(element, prev.next);

        size++;
    }

    @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;
    }

    @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();
    }
}