2-linked-lists.js

 
  
function LinkedList() {
  this.head = null;
  this.tail = null;
}

function Node(value, next, prev) {
  this.value = value;
  this.next = next;
  this.prev = prev;
}

LinkedList.prototype.addToHead = function(value) {
  let newNode = new Node(value, this.head, null);

  if (this.head) {
    this.head.prev = newNode;
  } else {
    this.tail = newNode;
  }
  this.head = newNode;
}

LinkedList.prototype.addToTail = function(value) {
  let newNode = new Node(value, null, this.tail);

  if (this.tail) {
    this.tail.next = newNode
  } else {
    this.head = newNode;
  }
  this.tail = newNode;
}

LinkedList.prototype.removeHead = function() {
  if (!this.head) {
    return null;
  }
  let val = this.head.value;

  this.head = this.head.next;

  if (this.head) {
    this.head.prev = null
  } else {
    this.tail = null
  }
  return val;
}

LinkedList.prototype.removeTail = function() {
  if (!this.tail) {
    return null;
  }
  let val = this.tail.value;

  this.tail = this.tail.prev;

  if (this.tail) {
    this.tail.next = null
  } else {
    this.head = null
  }
  return val;
}

LinkedList.prototype.search = function(searchValue) {
  let currentNode = this.head;

  while(currentNode) {
    if (currentNode.value === searchValue) return currentNode.value 
    currentNode = currentNode.next;
  }
  return null;
}

LinkedList.prototype.indexOf = function(searchValue) {
  let indexes = [];
  let currentIndex = 0;
  let currentNode = this.head;

  while(currentNode) {
    if (currentNode.value === searchValue) {
      indexes.push(currentIndex)
    }
    currentNode = currentNode.next;
    currentIndex++;
  }
  return indexes;
}

module.exports = {
    LinkedList
};