Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list. For example, Given 1->2->3->3->4->4->5, return 1->2->5. Given 1->1->1->2->3, return 2->3.

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) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        ListNode preHead(-1);
        preHead.next = head;
        ListNode* tmp = &preHead;
        while(tmp->next != NULL) {
            int val = tmp->next->val;
            
            ListNode* post = tmp->next;
            
            while(post->next != NULL and post->next->val == val) {
                post = post->next;
            }
            
            if(tmp->next != post) {
                tmp->next = post->next;
            } else {
                tmp = tmp->next;
            }
            
            
        }
        
        return preHead.next;
    }
};