82. Remove Duplicates from Sorted List II 删除排序链表中的重复数，重复的数全部删除

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

For example,
Given 1->2->3->3->4->4->5, return 1->2->5.

Given 1->1->1->2->3, return 2->3.

设置头辅助指针，非常简易。

/**
 * 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* newHead=new ListNode(-1);//设置辅助头结点
        newHead->next=head;
        ListNode* preHead=newHead;
        ListNode* curHead=head;
        while(curHead)
        {
            while(curHead->next&&curHead->val==curHead->next->val)
                curHead=curHead->next;
            if(preHead->next==curHead)
                preHead=preHead->next;
            else
            {
                preHead->next=curHead->next;
            }
            curHead=curHead->next;
        }
        return newHead->next;
    }
};