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;
}
};