Remove Duplicates from Sorted List

题目：

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

.

解析：

开始因为疏忽出现了两次runtime error情况，对于链表的问题一般就是如下情况

1. NULL->next

2. 指针是NULL，还用指针的val，p = NULL，p->val

/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* deleteDuplicates(ListNode* head) {
if(head == NULL || head->next == NULL)
return head;
ListNode *p = head;
while(p->next)
{
if(p->val == p->next->val)
p->next = p->next->next;
else
p = p->next;
}
return head;
}
};