/**
 * 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) {
        ListNode *node = head;
        while (node != NULL && node->next != NULL) {
            if (node->val != node->next->val) {
                node = node->next;
            } else {
                ListNode *tmp_node = node->next;
                node->next = node->next->next;
                delete tmp_node;
            }
        }
        return head;
    }
};