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)