remove-duplicates-from-sorted-list I&II——去除链表中重复项

I、Given a sorted linked list, delete all duplicates such that each element appear only once.

For example,
Given1->1->2, return1->2.
Given1->1->2->3->3, return1->2->3.

PS：遍历，而后记录pre，并删除后续重复node

 /**
  * 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) {
         ListNode *cur=head,*pre=NULL;
         while(cur!=NULL){
             if(pre==NULL){
                 pre=cur;
                 cur=cur->next;
                 continue;
             }
             ListNode *next=cur->next;
             if(pre->val==cur->val){
                 pre->next=next;
             }else
                 pre=cur;
             cur=next;
         }
         return head;
     }
 };

II、

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

For example,
Given1->2->3->3->4->4->5, return1->2->5.
Given1->1->1->2->3, return2->3.

删除所有重复项。

PS：循环比较next->val==cur->val，若next跳动则剔除cur至next之间的节点。否则右移left指针。

 /**
  * 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) return NULL;
         ListNode h(-);
         ListNode *res=&h;
         res->next=head;
         ListNode *cur=head,*pre=NULL,*left=res;
         while(cur!=NULL){
             ListNode* next=cur->next;
             while(next!=NULL&&cur->val==next->val){
                 next=next->next;
             }
             if(next==cur->next){
                 left=cur;
             }else{
                 left->next=next;
             }
             cur=next;
         }
         return res->next;
     }
 };