JZ76 删除链表中重复的结点

/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) :
        val(x), next(NULL) {
    }
};
*/
/*
方法一：
 时间复杂度：O(n)，空间复杂度O(1)
 
*/
class Solution {
public:
    ListNode* deleteDuplication(ListNode* pHead) {
        ListNode* cur = pHead;
        ListNode* pre = new ListNode(-1);  //在头节点之前建立一个结点
        ListNode* ans = pre; 
        pre->next = pHead;
        
        while(cur)
        {
            if(cur->next && cur->val == cur->next->val) 
            {
                cur = cur->next;
                while(cur->next && cur->val == cur->next->val)
                {
                    cur = cur->next;
                }
                pre->next = cur->next;
                cur = cur->next;
            }
            else
            {
                pre = cur;
                cur = cur->next;
            }
        }
        return ans->next;
    }
};