leetcode先刷_Remove Duplicates from Sorted List II

删除重复节点列表中的，假设所有val如果仅仅是为了保持一个非常easy。应承担重复val节点被删除话。要保持pre节点，每当你想保存这pre问题节点。应该head节点可以被取出，好了，没问题边境控制。

class Solution {
public:
    ListNode *deleteDuplicates(ListNode *head) {
        if(head == NULL || head->next == NULL)
            return head;
        ListNode *pre = NULL, *start = head, *end;
        while(start){
            while(start&&start->next&&start->val != start->next->val){
                pre = start;
                start = start->next;
            }
            end = start;
            while(end&&end->next&&end->val == end->next->val)
                end = end->next;
            if(end!=start&&end){
                if(pre)
                    pre->next = end->next;
                else{
                    head = end->next;
                }
            }else{
                break;
            }
            start = end->next;
        }
        return head;
    }
};