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.
public ListNode deleteDuplicates(ListNode head) { if (head == null) return head; ListNode p1 = head; while (p1.next != null) { if (p1.val == p1.next.val) { p1.next = p1.next.next; } else { p1 = p1.next; } } return head; }比较简答，LeetCode官方链接
public ListNode deleteDuplicates(ListNode head) { ListNode current = head; while (current != null && current.next != null) { if (current.next.val == current.val) { current.next = current.next.next; } else { current = current.next; } } return head; }这里就是把为空的判断放在了while循环里，看起来代码时简单了很多，但是我觉得这样子还不好，每次循环的时候都要去判断一下。
