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.
1->1->2
1->2
1->1->2->3->3
1->2->3
删除一个链表中的重复元素
原文：http://www.cnblogs.com/yangscode/p/5032458.html
