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function Node(element) {
    this.element = element;
    this.next = null;
}

function LList() {
    this.head = new Node("head");
    this.find = find;
    // for circular llist
    // this.head.next = this.head;
    this.insert = insert;
    this.display = display;
    this.findPrevious = findPrevious;
    this.remove = remove;
}

function advance(n) {
    // the current node is moved n nodes forward in the list.
    var currNode = this.head,
        i = 0;

    this.remove(this.head);

    while (i < n) {
        if (!(this.head.next == null)) {
            this.head = this.head.next;
            i++;
        }
    }

    this.insert(currNode, this.head);
}

function remove(item) {
    var prevNode = this.findPrevious(item);
    if (!(prevNode.next == null)) {
        prevNode.next = prevNode.next.next;
    }
}

function findPrevious(item) {
    var currNode = this.head;
    while (!(currNode.next == null) &&
        (currNode.next.element != item)) {
        currNode = currNode.next;
    }
    return currNode;
}

function display() {
    var currNode = this.head;
    while (!(currNode.next == null)) {
        console.log(currNode.next.element);
        currNode = currNode.next;
    }

    // for circular linked list
    // while (!(currNode.next == null) &&
    //     !(currNode.next.element == "head")) {
    //     print(currNode.next.element);
    //     currNode = currNode.next;
    // }
}

function find(item) {
    var currNode = this.head;
    while (currNode.element != item) {
        currNode = currNode.next;
    }
    return currNode;
}

function insert(newElement, item) {
    var newNode = new Node(newElement);
    var current = this.find(item);
    newNode.next = current.next;
    current.next = newNode;
}


var cities = new LList();
cities.insert("Conway", "head");
cities.insert("Russellville", "Conway");
cities.insert("Carlisle", "Russellville");
cities.insert("Alma", "Carlisle");
cities.display();
console.log();
cities.remove("Carlisle");
cities.display();

function Node(element) {
   this.element = element;
   this.next = null;
   this.previous = null;
}

function LList() {
   this.head = new Node("head");
   this.find = find;
   this.insert = insert;
   this.display = display;
   this.remove = remove;
   this.findLast = findLast;
   this.dispReverse = dispReverse;
}

function dispReverse() {
   var currNode = this.head;
   currNode = this.findLast();
   while (!(currNode.previous == null)) {
      console.log(currNode.element);
      currNode = currNode.previous;
   }
}

function findLast() {
   var currNode = this.head;
   while (!(currNode.next == null)) {
      currNode = currNode.next;
   }
   return currNode;
}

function remove(item) {
   var currNode = this.find(item);
   if (!(currNode.next == null)) {
       currNode.previous.next = currNode.next;
       currNode.next.previous = currNode.previous;
       currNode.next = null;
       currNode.previous = null;
   }
}

// findPrevious is no longer needed
/*function findPrevious(item) {
   var currNode = this.head;
   while (!(currNode.next == null) && 
           (currNode.next.element != item)) {
      currNode = currNode.next;
   }
   return currNode;
}*/

function display() {
   var currNode = this.head;
   while (!(currNode.next == null)) {
      console.log(currNode.next.element);
      currNode = currNode.next;
   }
}

function find(item) {
   var currNode = this.head;
   while (currNode.element != item) {
      currNode = currNode.next;
   }
   return currNode;
}

function insert(newElement, item) {
   var newNode = new Node(newElement);
   var current = this.find(item);
   newNode.next = current.next;
   newNode.previous = current;
   current.next = newNode;
}
   

var cities = new LList();
cities.insert("Conway", "head");
cities.insert("Russellville", "Conway");
cities.insert("Carlisle", "Russellville");
cities.insert("Alma", "Carlisle");
cities.display();
console.log();
cities.remove("Carlisle");
cities.display();
console.log();
cities.dispReverse();