/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 *  ListNode(int x): val(x), next(nullptr) {};
 * };
 */

class Solution {
public:
    /**
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    ListNode* deleteDuplicates(ListNode* head) {
        // write code here
        ListNode* slow = head;
        ListNode* fast = head;
        
        while(fast != nullptr){
            while(fast != nullptr && fast->val == slow->val){
                fast = fast->next;
            }
            slow->next = fast;
            slow = fast;
        }
        return head;
    }
};