LeetCode 82. Remove Duplicates from Sorted List II

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class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        if (!head) return head;
        ListNode* dummyHead = new ListNode(0, head);
        ListNode* curr = dummyHead;
        while (curr->next && curr->next->next) {
            if (curr->next->val == curr->next->next->val) {
                int x = curr->next->val;
                curr->next = curr->next->next->next;
                while(curr->next && curr->next->val == x)
                    curr->next = curr->next->next;
            } else {
                curr = curr->next;
            }
        }
        return dummyHead->next;
    }
};
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class Solution {
public:
    ListNode* deleteDuplicates(ListNode* head) {
        if (!head || !head->next) return head;
        if (head->val != head->next->val) {
            head->next = deleteDuplicates(head->next);
            return head;
        }
        int x = head->val;
        head = head->next->next;
        while (head != nullptr && head->val == x)
            head = head->next;
        return deleteDuplicates(head);
    }
};