class Solution { public: ListNode *deleteDuplicates(ListNode *head) { if(!head) return NULL; ListNode* firstNode = head; ListNode* currentNode = head; ListNode* nextNode = head; while(currentNode->next){ if(currentNode->val == currentNode->next->val){ if(currentNode->next->next){ currentNode->next = currentNode->next->next; }else{ currentNode->next = NULL; } }else{ currentNode = currentNode->next; } } return head; } };