[Leetcode] Remove Duplicates from Sorted List

Remove Duplicates from Sorted List

Given a sorted linked list, delete all duplicates such that each element appear only once.

Analysis:  
straightforward question, if it's a sorted array we don't need hashtable but keep comparing next node with current node to remove duplicates.

Solution: 
ListNode *deleteDuplicates(ListNode *head) {

        ListNode *dummy = new ListNode(0);        
        dummy->next = head;               // use dummy head to avoid taking care of first node later
        ListNode *current = head;         // use single pointer to traverse the list

        while(current)               // two while loops, it still takes O(n) cuz every node once is visited once
        {
            while(current->next)   // In this loop comparing adjacent nodes to remove duplicates
            {
               if(current->next->val == current->val)  // Removing next node cuz it's a duplicate
               {
                   ListNode *temp = current->next;
                   current->next = current->next->next;
                   
                   delete temp;
                   continue;
               }
               else
               {
                   break;                         // Or the next node is NOT a duplicate, break and move forward
               }
            }  
            current = current->next;

        }        
        return dummy->next;           // return next element of dummy header which is beginning of new list


    }