# 删除排序链表中的重复元素
存在一个按升序排列的链表，给你这个链表的头节点 head ，请你删除所有重复的元素，使每个元素 只出现一次 。
返回同样按升序排列的结果链表。
示例 1：
输入：head = [1,1,2]
输出：[1,2]
示例 2：
输入：head = [1,1,2,3,3]
输出：[1,2,3]
提示：
- 链表中节点数目在范围
[0, 300] 内 -100 <= Node.val <= 100- 题目数据保证链表已经按升序排列
以下错误的选项是？
## aop
### before
```cpp
#include
using namespace std;
struct ListNode
{
int val;
ListNode *next;
ListNode(int x) : val(x), next(NULL) {}
};
```
### after
```cpp
```
## 答案
```cpp
class Solution
{
public:
ListNode *deleteDuplicates(ListNode *head)
{
if (!head || !head->next)
return head;
head->next = deleteDuplicates(head->next);
if (head->val != head->next->val)
head = head->next;
return head;
}
};
```
## 选项
### A
```cpp
class Solution
{
public:
ListNode *deleteDuplicates(ListNode *head)
{
if (head == NULL || head->next == NULL)
return head;
ListNode *p = head;
ListNode *q = head->next;
while (p->next != NULL)
{
if (p->val == q->val)
{
if (q->next == NULL)
p->next = NULL;
else
{
p->next = q->next;
q = q->next;
}
}
else
{
p = p->next;
q = q->next;
}
}
return head;
}
};
```
### B
```cpp
class Solution
{
public:
ListNode *deleteDuplicates(ListNode *head)
{
ListNode *cur = head;
while (cur != NULL)
{
ListNode *rear = cur->next;
if (rear == NULL)
return head;
if (cur->val == rear->val)
cur->next = rear->next;
else
cur = cur->next;
}
return head;
}
};
```
### C
```cpp
class Solution
{
public:
ListNode *deleteDuplicates(ListNode *head)
{
if (head == NULL)
return head;
ListNode *ptr{head};
while (ptr->next != NULL)
{
if (ptr->val == ptr->next->val)
{
ListNode *p = ptr->next;
ptr->next = p->next;
delete p;
}
else
{
ptr = ptr->next;
}
}
return head;
}
};
```