83、删除链表重复节点

Given a sorted linked list, delete all duplicates such that each element appear onlyonce.

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 || head.next == null)
    return head;
  ListNode slow = head;
  ListNode fast = head.next;
  while (slow != null && fast != null) {
    if (slow.val != fast.val) {
      slow = fast;
      fast = fast.next;
    } else {
      slow.next = fast.next;
      fast = fast.next;
    }
  }
  return head;
}