单链表的实现扩充

之前我们用2种方法实现了单链表，现在我们将再增加一种方法。

function LinkedList() {
	var Node = function (value) {
		this.value = value;
		this.next = null;
	}

	var head = null;
	var length = 0; 	

	/* 1）使用一个辅助函数来实现递归*/
	this.append1 = function (value) {
		var new_node = new Node(value);
		if(head == null) {
			head = new_node;
		} else {
			appendNode(head, new_node);
		} 

		length++;

		function appendNode(parent, new_node) {
			if(parent.next == null) {
				parent.next = new_node;
			} else {
				insertNode(parent.next, new_node);
			} 
		}
	}

	/* 2）不使用辅助函数来实现递归 */
	this.append2 = function (value, parent, new_node) {
		/*
			使用parent保存中间节点
		*/
		var new_node = new_node || (new Node(value));
		if(head == null) {
			head = new_node;
			length++;
		} else {
			var current = parent || head;
			if(current.next == null) {
				current.next = new_node;
				length++;
			} else {
				this.append2(value, current.next, new_node);
			}	
		}
	}

	/* 3) 不使用递归*/
	this.append3 = function (value) {
		var new_node = new Node(value);
		if(head == null) {
			head = new_node;
		} else {
			var current = head;
			while(current.next != null) {
				current = current.next;
			}

			current.next = new_node;
		}

		length++;
	}


	this.getHead = function () {
		return head;
	}

	/*一个遍历函数*/
	this.traverse = function () {
		var current = head;
		while(current != null) {
			console.log(current.value);
			current = current.next;
		}
	}

	this.size = function () {
		return length;
	}
}


var arr = [8, 7, 4, 3, 2, 9, 20];
var linked_list = new LinkedList();
for(var i=0; i<arr.length; ++i) {
	linked_list.append2(arr[i]);
}

var head = linked_list.getHead();