Given a sorted linked list, delete all duplicates such that each element appear only once.
For example,
Given 1->1->2, return 1->2.
Given 1->1->2->3->3, return 1->2->3.
题意：给一个有序的链表，让我们去掉重复的节点。
java代码：
public ListNode deleteDuplicates(ListNode head) {
ListNode h1 = head;
while(h1 != null && h1.next != null){
if (h1.val == h1.next.val) {
h1.next = h1.next.next;
}else {
h1 = h1.next;
}
}
return head;
}
