Leetcode: Remove Duplicates from Sorted List II

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.

分析：要充分利用sorted的性质，如果是sorted的那么重复的元素是连接在一起的，实现细节要注意删除node和未删除node指针向后移动的不同。

class Solution {
public:
    ListNode *deleteDuplicates(ListNode *head) {
        if(head == NULL || head->next == NULL) return head;
        
        int dup = INT_MAX;
        ListNode *dummy = new ListNode(-1);
        dummy->next = head;
        
        for(ListNode *prev = dummy, *p = head; p;  p = prev->next){
            if(p->val == dup){
                prev->next = p->next;
            }else if(p->next && p->val == p->next->val){
                dup = p->val;
                prev->next = p->next;
            }else prev = p;
        }
        return dummy->next;
    }
};