# [3217\. Delete Nodes From Linked List Present in Array](https://leetcode.com/problems/delete-nodes-from-linked-list-present-in-array/)

:::spoiler Hint

/**
 * 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)
    {
        // Create an unordered set from the input vector nums for quick lookup
        // Create a dummy node to serve as the new list's head
        // Initialize a pointer to the dummy node for constructing the new list
        // Initialize a pointer to traverse the original list

        // Traverse the original list
        while ()
        {
            // If the current node's value is not in the set, add it to the new list
            if ()
            {
                // Create a new node with the current node's value and link it to the new list
                // Move the prev pointer to the newly created node
            }
            // Move to the next node in the original list

:::

:::spoiler Solution

/**
 * 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;
    }
};

- 時間複雜度：$O(m + n)$
- 空間複雜度：$O(n)$
:::