给定一个排序链表，删除所有重复的元素，使得每个元素只出现一次。
示例 1:
输入: 1->1->2 输出: 1->2
示例 2:
输入: 1->1->2->3->3 输出: 1->2->3
/**
* Definition for singly-linked list.
* function ListNode(val) {
* this.val = val;
* this.next = null;
* }
*/
/**
* @param {ListNode} head
* @return {ListNode}
*/
var deleteDuplicates = function(head) {
if (head === null) return null;
var nodePrev = null;
var node = head;
var singlePrev = head;
var bStart = true;
while (node !== null) {
if (nodePrev !== null && node.val != nodePrev.val) {
singlePrev.next = node;
singlePrev = node;
}
nodePrev = node;
node = node.next;
}
singlePrev.next = null;
return head;
};