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

.
Solution:
Code:

<span style="font-size:14px;">/**
* Definition for singly-linked list.
* struct ListNode {
*     int val;
*     ListNode *next;
*     ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode *deleteDuplicates(ListNode *head) {
if (head == NULL || head->next == NULL) return head;
bool duplicate;
while (head != NULL && head->next != NULL) {
duplicate = false;
while (head != NULL && head->next != NULL) {
if (head->val != head->next->val) break;
duplicate = true;
head = head->next;
}
if (!duplicate) break;
head = head->next;
}
if (head == NULL || head->next == NULL) return head;
ListNode *begin = head, *end = head;
head = head->next;
while (head != NULL && head->next != NULL) {
duplicate = false;
while (head != NULL && head->next != NULL) {
if (head->val != head->next->val) break;
duplicate = true;
head = head->next;
}
if (!duplicate) {
end->next = head;
end = head;
}
head = head->next;
}
if (head != NULL)
end->next = head;
else
end->next = NULL;
return begin;
}
};</span>