double-linked-list.js

class DoubleLinkedList extends LinkedList {
  tail = null;

  createNode(element) {
    return { element, next: null, prev: null };
  }

  push(element) {
    const node = this.createNode(element);

    if (!this.head) {
      this.head = node;
    } else {
      const current = this.getNodeAt(this.size - 1);
      current.next = node;
      node.prev = current;
    }
    
    this.tail = node;

    this.size += 1;
    return this.size;
  }

  insert(element, index = 0) {
    if (index > this.size) return false;

    const node = this.createNode(element);

    if (index === 0) {
      if (this.head) {
        node.next = this.head;
        this.head.prev = node;
      } else {
        this.tail = node;
      }
      this.head = node;
    } else if (index === this.size) {
      this.tail.next = node;
      node.prev = this.tail;
      this.tail = node;
    } else {
      const current = this.getNodeAt(index);
      const prev = current.prev;

      prev.next = node;
      current.prev = node;
      node.prev = prev;
      node.next = current;
    }

    this.size = this.size + 1;

    return true;
  };

  remove(index = 0) {
    if (index > this.size) return null;

    let removedNode = this.head;

    if (index === 0) {
      this.head = removedNode.next;
      if (this.size === 1) {
        this.tail = null;
      } else {
        this.head.prev = null;
      }
    } else if (index === this.size - 1) {
      removedNode = this.tail;
      this.tail = removedNode.prev;
      this.tail.next = null;
    } else {
      removedNode = this.getNodeAt(index);
      const previous = removedNode.prev;
      const next = removedNode.next;

      previous.next = next;
      next.prev = previous;
    }

    this.size = this.size - 1;
    return removedNode;
  };

  reverse() {
    let current = this.head;
    this.head = this.tail;
    this.tail = current;
    
    for(let i = 0; i<this.size; i++) {
      const prev = current.prev;
      const next = current.next;
      
      current.prev = next;
      current.next = prev;
      current = next;
    }
  }
}