83. Remove Duplicates from Sorted List

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

For example,
Given 1->1->2, return 1->2.
Given 1->1->2->3->3, return 1->2->3.

/**
 * 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){
            return head;
        }
        
        
        ListNode* l1 = head;
        
        while(l1 && l1->next)
        {
            if(l1->val != l1->next->val){
                l1 = l1->next;
            }else{
                ListNode* p = l1->next->next;
                l1->next = p;
            }
            
        }
        return head;
    }
};