int val;

ListNode *next;

ListNode(int x) : val(x), next(NULL) {}

public:

ListNode* deleteDuplicates(ListNode* head) {

ListNode fakeHead(-1);

fakeHead.next = head;

ListNode *pre = &fakeHead;

while(head) {

ListNode *next = head->next;

if (next == NULL || next->val != head->val) {

pre = head;

head = head->next;

continue;

}

while (next != NULL && next->val == head->val) {

head->next = next->next;

delete next;

next = head->next;

}

pre->next = head->next;

delete head;

head = pre->next;

}

return fakeHead.next;

}