【链表】Remove Duplicates from Sorted List II（三指针）

题目：

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

For example,
Given

1->2->3->3->4->4->5

, return

1->2->5

.
Given

1->1->1->2->3

, return

2->3

.

思路：

找到重复的项，记录下他们前面的节点，然后删除。

/**
* 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||head.next==null){
return head;
}
var l=head,r=head.next,rpre=null;
var tempHead=new ListNode(0);
tempHead.next=head;
var pre=tempHead;
while(r!=null){
if(l.val==r.val){
while(r!=null&&r.val==l.val){
rpre=r;
r=r.next;
}
pre.next=r;
if(r==null){
return tempHead.next;
}else{
l=r;
r=r.next;
}
}else{
l=l.next;
r=r.next;
pre=pre.next;
}
}

return tempHead.next;
};