3217. Delete Nodes From Linked List Present in Array

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* modifiedList(vector<int>& nums, ListNode* head)
    {
        unordered_set<int> st(nums.begin(), nums.end());

        ListNode* dummy = new ListNode();
        ListNode* prev = dummy;
        ListNode* cur = head;

        while (cur)
        {
            if (!st.count(cur->val))
            {
                prev->next = new ListNode(cur->val);
                prev = prev->next;
            }
            cur = cur->next;
        }
        return dummy->next;
    }
};

• T: $O(M + N)$
• S: $O(N)$