【Lintcode】113.Remove Duplicates from Sorted List II

题目：

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

 Example

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

题解：

Solution 1 ()

class Solution {
public:
    ListNode *deleteDuplicates(ListNode *head) {
        if (head == nullptr) {
            return head;
        }
        ListNode* dummy = new ListNode(-1);
        
        dummy->next = head; 
        head = dummy;
        while (head->next != nullptr && head->next->next != nullptr) {
            if (head->next->val == head->next->next->val) {
                int value = head->next->val;
                while (head->next != nullptr && head->next->val == value) {
                    head->next = head->next->next;
                }
            } else {
                head = head->next;
            }
        }
        
        return dummy->next;
    }
};

　　二级指针

Solution 2 （）

class Solution {
public:
    ListNode *deleteDuplicates(ListNode *head) {
        if (head == nullptr || head->next == nullptr) {
            return head;
        }
        ListNode **t = &head;
        while (*t) {
            if ((*t)->next && (*t)->next->val == (*t)->val) {
                ListNode *tmp = *t;
                while (tmp && (*t)->val == tmp->val) {
                    tmp = tmp->next;
                }
                *t = tmp;
            } else {
                t = &((*t)->next);
            }
        }
        
        return head;
    }
};