// https://www.freecodecamp.org/learn/coding-interview-prep/data-structures/create-a-doubly-linked-list

var Node = function (data, prev) {
  this.data = data;
  this.prev = prev;
  this.next = null;
};
var DoublyLinkedList = function () {
  this.head = null;
  this.tail = null;
  // Only change code below this line
  this.add = (element) => {
    const node = new Node(element, this.tail);
    if (this.head === null) {
      this.head = node;
      this.tail = node;
    } else {
      this.tail.next = node;
      this.tail = node;
    }
  };

  this.remove = (element) => {
    let prevNode = null;
    let currentNode = this.head;
    while (currentNode !== null && currentNode.data !== element) {
      prevNode = currentNode;
      currentNode = currentNode.next;
    }
    if (currentNode === null || currentNode.data !== element) {
      return;
    }
    if (prevNode === null) {
      this.head = currentNode.next;
    } else {
      prevNode.next = currentNode.next;
    }
    if (currentNode.next === null) {
      this.tail = prevNode;
    } else {
      const nextNode = currentNode.next;
      nextNode.prev = prevNode;
    }
    return currentNode.element;
  };
  // Only change code above this line
};