[leetcode] Remove Duplicates from Sorted List II

From : https://leetcode.com/problems/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

.

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Linked List

Solution :

/**
* 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) return NULL;
int v = head->val;
ListNode *th = new ListNode(0), *pre, *p;
th->next = head;
pre = th;
p = head;
while(p) {
if(p->next && p->next->val == v) {
while(p && p->val == v) {
pre->next = p->next;
delete p;
p = pre->next;
}
} else {
pre = p;
p = p->next;
}
if(p) v=p->val;
}
p = th->next;
delete th;
return p;
}
};