Remove Duplicates from Sorted List

删除一个有序单链表的重复节点

For example,
Given 1->1->2, return 1->2.
Given 1->1->2->3->3, return 1->2->3.

思路：两个指针，一前一后，前面指针的值与后面指针的值相等就往前，直到不同，后指针的下一个节点指向前指针，然后继续。
注意一下边界：

• 头指针为空
• 链表只有一个节点

• 尾部需要处理

  class Solution {public:  ListNode *deleteDuplicates(ListNode *head)  {      if (!head || !head->next)      {          return head;      }      ListNode* forward = head->next;      ListNode* backward = head;      while (forward-> next!= NULL)      {          if (forward->val == backward->val)          {              forward = forward->next;          }          else          {              backward->next = forward;              backward = forward;              forward = forward->next;          }      }      if (backward->val == forward->val)      {          backward->next = NULL;      }      else      {          backward->next = forward;      }      return head;  }};

来自为知笔记(Wiz)

来源：https://www.cnblogs.com/flyjameschen/p/4341304.html