难以理解反转链表的工作原理

Question

我正在反转链表。我知道这是一项微不足道的任务，但我有一个理解问题。我在 JavaScript

中使用 class 语法

class LinkedList {
    constructor(value) {
        this.head = {
            value: value,
            next: null
        };
        this.tail = this.head;
        this.length = 1;
    }
    append(value) {
      const newNode = {
        value: value,
        next: null
      }
      this.tail.next = newNode;
      this.tail = newNode;
      this.length++;
      return this;
    }
    reverse() {
      if (!this.head.next) {
        return this.head;
      }
      let first = this.head;
      this.tail = this.head;
      let second = first.next;
      let temp = null

      while(second) {
        temp = second.next;
        second.next = first;
        first = second;
        second = temp;

        console.log('first', first)
      }

      this.head.next = null;
      console.log('first after', first)
      this.head = first;
      return this
    }
}
let myLinkedList = new LinkedList(5);
myLinkedList.append(1)
myLinkedList.append(99)
myLinkedList.reverse()

我无法理解的是：在 while 循环的最后一次迭代之后，first 变量应该指向这个对象（它是 console.log('first', first)）：

{ value: 99,
  next: { value: 1, next: { value: 5, next: [Circular] } } }

然而，循环结束后，first开始指向这个，它给了我们正确的答案（它是 console.log('first after', first)):

{ value: 99,
  next: { value: 1, next: { value: 5, next: null } } }

我什至尝试画图，但仍然无法理解为什么会这样（为什么first.next.next.next开始指向null）

Answer 1

这是因为 this.head.next = null;.
行 first.next.next.next 和 this.head 指向同一个节点：5.

以下是您的代码以及一些额外的注释：

    reverse() {
      // At the start of the invocation, the linked list will be:
      // head: 5
      // (mid): 1
      // tail: 99

      if (!this.head.next) {
        return this.head;
      }
      let first = this.head;
      this.tail = this.head;
      let second = first.next;
      let temp = null

      while(second) {
        temp = second.next;
        second.next = first;
        first = second;
        second = temp;

        console.log('first', first)
      }

      // At this point, the `next` pointer of each node is updated together
      // with `this.tail`, but `this.head` still refers to the previous head (now tail).
      // `this.head` and `first.next.next.next` reference the same node '5'.

      this.head.next = null;
      console.log('first after', first)

      // Only after this assignment will the head be updated, resulting in the following linked list:
      // head: 99
      // (mid): 1
      // tail: 5
      this.head = first;

      return this
    }

难以理解反转链表的工作原理

trouble understanding how reversing a linked list works

javascript

reverse

linked-list