给定一个排序链表，删除所有重复的元素只留下原链表中没有重复的元素。
样例
给出 1->2->3->3->4->4->5->null，返回 1->2->5->null
给出 1->1->1->2->3->null，返回 2->3->null
代码
/**
* Definition for ListNode
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) {
* val = x;
* next = null;
* }
* }
*/
public class Solution {
/**
* @param head: head is the head of the linked list
* @return: head of the linked list
*/
public ListNode deleteDuplicates(ListNode head) {
if (head == null || head.next == null) {
return head;
}
ListNode dummy = new ListNode(0);
dummy.next = head;
head = dummy;
while (head.next != null && head.next.next != null) {
if (head.next.val == head.next.next.val) {
int val = head.next.val;
// val 记录的是重复元素的值，下面的 while 循环会跳过所有的重复元素的值
while (head.next != null && head.next.val == val) {
head.next = head.next.next;
}
} else {
head = head.next;
}
}
return dummy.next;
}
}
