[JS与链表]双向链表

class DoublyLinkedListNode {
  constructor(value) {
    this.value = value;
    this.next = null;
    this.prev = null;
  }
}
 
class DoublyLinkedList {
  constructor() {
    this.head = null;
    this.tail = null;
    this.length = 0;
  }
 
  append(value) {
    const newNode = new DoublyLinkedListNode(value);
    if (this.length === 0) {
      this.head = newNode;
      this.tail = newNode;
    } else {
      this.tail.next = newNode;
      newNode.prev = this.tail;
      this.tail = newNode;
    }
    this.length++;
    return this;
  }
 
  delete(value) {
    if (this.length === 0) return null;
 
    let current = this.head;
    while (current.value !== value) {
      if (current.next === null) return null;
      current = current.next;
    }
 
    if (current === this.head) {
      if (this.length === 1) {
        this.head = null;
        this.tail = null;
      } else {
        this.head = this.head.next;
        this.head.prev = null;
        current.next = null;
      }
    } else if (current === this.tail) {
      this.tail = current.prev;
      this.tail.next = null;
      current.prev = null;
    } else {
      current.prev.next = current.next;
      current.next.prev = current.prev;
      current.next = null;
      current.prev = null;
    }
 
    this.length--;
    return current.value;
  }
}

这段代码实现了一个简单的双向链表，包含了添加节点和删除节点的基本操作。添加节点时，如果链表为空，则新节点既是头节点也是尾节点；如果不为空，则新节点成为尾节点，并且其前驱指向当前的尾节点。删除节点时，需要考虑节点位于头部、尾部还是中间的不同情况，并更新相关节点的prev和next指针。