Linked List

Linked List - Stack

// HOMEWORK WEEK 3, day 1 -  Linked list

/*

prepend(data) - insert a new node with the value data at the beginning of the list
append(data) - insert a new node with the value data at the end of the list
pop_front(callback) - removes the first element of the list and invokes callback with the data value passed as the parameter to callback
pop_back(callback) - removes the last element of the list and invokes callback with the data value passed as the parameter to callback

*/

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

var newNode = function(data) {
	this.data = data;
	this.prev = null;
}

LinkedList.prototype.append = function(data) {
	var node = new newNode(data);
	if (this.head === null) {
		this.head = node;
		this.prev = null;
	}
	else {
		var temp = this.head;
		while (temp.next !== null) {
			temp = temp.next;
		}
		temp.next = node;
	}
	this.numItems++
}

LinkedList.prototype.prepend = function ( data ) {
	var node = new newNode( data );
	
	// sets next node to the head;
	node.next = this.head;
	// FIX - get circular --- this.head.prev = node;
	// sets new node as head;
	this.head = node;
}

LinkedList.prototype.pop_front = function ( callback ) {
	// cache first element
	var popped = this.head;
	if( !popped ) return callback ("stack is empty");
	// set child to head
	this.head = this.head.next;
	// return first element in callback
	callback ( null, popped );
}

LinkedList.prototype.pop_back = function ( callback ) {
	var temp = this.head || undefined;
	
	if( !temp ) return callback ("stack is empty");

	while( temp.next.next !== null ) {
		temp = temp.next;
	}

	var popped = temp.next;
	temp.next = null;
	callback ( null, popped );
}


var test = function( err, el ) {
	if( err ) {
		console.log (err);
	} else {
		console.log ( el.data + ' has been removed;')
	}	
}


//////////////////////////////////////////////////////////////////////////////////////////////////////////////
// TEST CODE
//////////////////////////////////////////////////////////////////////////////////////////////////////////////

// creates a new double linked list
var dLL = new LinkedList();

dLL.pop_back(test);

dLL.append("hello");
dLL.append("class");
dLL.append("world");
dLL.append("try");

// insert a new node with the value data at the beginning of the list
dLL.prepend("first");

// removes the first element of the list and invokes callback with the data value passed as the parameter to callback
dLL.pop_front (test);
dLL.pop_back(test);


console.log(dLL.head);