Remove Duplicates from Sorted List II.cpp

/**
 * 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;
        ListNode * p = head;
        while(p->next!=NULL && p->val == p->next->val){
             p=p->next;
        }

        if(p!=head){
            while(head!=p->next)
            {
                ListNode * tmp = head;
                head=head->next;
                free(tmp);
            }
    
            return deleteDuplicates(p->next);
        }

        head->next=deleteDuplicates(head->next);
        return head;
        
    }
};