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(-1);
        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;
    }
};