删除排序链表中的重复元素

1->1->2->null

1->2->null

1->1->2->3->3->null

1->2->3->null

/**
* Definition of ListNode
* class ListNode {
* public:
*     int val;
*     ListNode *next;
*     ListNode(int val) {
*         this->val = val;
*         this->next = NULL;
*     }
* }
*/
class Solution {
public:
/**
* @param head: The first node of linked list.
* @return: head node
*/
ListNode *deleteDuplicates(ListNode *head) {
// write your code here
if(head==NULL)
return NULL;
if(head->next==NULL)
return head;
ListNode*l2 =head;
ListNode* l1 = head->next;
for(;l1!=NULL;l1=l1->next){
if(l1->val!=head->val){
head->next = l1;
head = l1;
}
}
return l2;
}
};