链表

• 链表中表示一个节点的类

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

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

element表示节点的值，next表示当前节点的下一个节点

• 全局变量

    private int size;
    private Node<E> first;

size表示链表的长度，first表示链表的头节点

• 获取索引节点

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

从头节点遍历获取到index节点，返回index节点的node

• 修改index节点的值

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

先获取index节点的node，然后修改node.element

• 添加节点

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

index=0表示添加头节点，直接初始化first
在指定index位置添加节点，就是在index-1和index+1中间位置添加element，index-1.next=index.next=index+1.next

• 删除索引位置节点

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

index=0表示删除头节点，让first.next等于first
index非0，先获取index-1节点的位置（index的前驱），让(index-1).next=index.next前驱节点.next=后继节点，代码node = prev.nextnode就是index节点

• 获取index位置元素

   public int indexOf(E element) {
        if (element == null) {
            Node<E> node = first;
            for (int i = 0; i < size; i++) {
                if (node.element.equals(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 -1;
    }

从first节点开始便利到size，进行equals()判断

• index校验

    private void checkRangeForAdd(int index) {
        if (index < 0 || index > index) {
            indexOutOfBoundException(index);
        }
    }

    private void checkRange(int index) {
        if (index < 0 || index >= index) {
            indexOutOfBoundException(index);
        }
    }

• 遍历链表

       Node node = first;
        for (int i = 0; i < size; i++) {
            node = node.next;
        }

从first开始for编列到size

       Node node = first;
       while (node != null) {
            node = node.next;
        }

从first开始遍历，只有first.next!=null就一直while()

• 反转链表

    public ListNode reverseList(ListNode head) {
        if (head == null || head.next == null) return head;

        ListNode newHead = null;
        while (head != null) {
            ListNode tmp = head.next;
            head.next = newHead;
            newHead = head;
            head = tmp;
        }

        return newHead;
    }

• 判断是否环形链表

    public boolean hasCycle(ListNode head) {
        if (head == null || head.next == null) return false;

        ListNode slow = head;
        ListNode fast = head.next;
        while (fast != null && fast.next != null) {
            slow = slow.next;
            fast = fast.next.next;

            if (slow == fast) return true;
        }
        return false;
    }

• 删除链表中的节点

    public void deleteNode(ListNode node) {
        node.val = node.next.val;
        node.next = node.next.next;
    }