83. Remove Duplicates from Sorted List

/**
 * 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 == nullptr){
            return nullptr;
        }
        ListNode* dummyNode = new ListNode(-1);
        dummyNode -> next  = head;
        head = dummyNode;
        
        while(head -> next != nullptr && head -> next -> next != nullptr){
            if(head -> next -> val == head -> next -> next -> val){                              
                head -> next = head -> next -> next;                   
            }                
            else{
               head = head -> next; 
            }
                       
        }
        return dummyNode -> next;
    }
};