Delete Nodes From Linked List Present in Array
<p>You are given an array of integers <code>nums</code> and the <code>head</code> of a linked list. Return the <code>head</code> of the modified linked list after <strong>removing</strong> all nodes from the linked list that have a value that exists in <code>nums</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">nums = [1,2,3], head = [1,2,3,4,5]</span></p>

<p><strong>Output:</strong> <span class="example-io">[4,5]</span></p>

<p><strong>Explanation:</strong></p>

<p><strong><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/3200-3299/3217.Delete%20Nodes%20From%20Linked%20List%20Present%20in%20Array/images/linkedlistexample0.png" style="width: 400px; height: 66px;" /></strong></p>

<p>Remove the nodes with values 1, 2, and 3.</p>
</div>

<p><strong class="example">Example 2:</strong></p>

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">nums = [1], head = [1,2,1,2,1,2]</span></p>

<p><strong>Output:</strong> <span class="example-io">[2,2,2]</span></p>

<p><strong>Explanation:</strong></p>

<p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/3200-3299/3217.Delete%20Nodes%20From%20Linked%20List%20Present%20in%20Array/images/linkedlistexample1.png" style="height: 62px; width: 450px;" /></p>

<p>Remove the nodes with value 1.</p>
</div>

<p><strong class="example">Example 3:</strong></p>

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">nums = [5], head = [1,2,3,4]</span></p>

<p><strong>Output:</strong> <span class="example-io">[1,2,3,4]</span></p>

<p><strong>Explanation:</strong></p>

<p><strong><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/3200-3299/3217.Delete%20Nodes%20From%20Linked%20List%20Present%20in%20Array/images/linkedlistexample2.png" style="width: 400px; height: 83px;" /></strong></p>

<p>No node has value 5.</p>
</div>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 10<sup>5</sup></code></li>
	<li><code>1 &lt;= nums[i] &lt;= 10<sup>5</sup></code></li>
	<li>All elements in <code>nums</code> are unique.</li>
	<li>The number of nodes in the given list is in the range <code>[1, 10<sup>5</sup>]</code>.</li>
	<li><code>1 &lt;= Node.val &lt;= 10<sup>5</sup></code></li>
	<li>The input is generated such that there is at least one node in the linked list that has a value not present in <code>nums</code>.</li>
</ul>
Array; Hash Table; Linked List
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode modifiedList(int[] nums, ListNode head) {
        Set<Integer> s = new HashSet<>();
        for (int x : nums) {
            s.add(x);
        }
        ListNode dummy = new ListNode(0, head);
        for (ListNode pre = dummy; pre.next != null;) {
            if (s.contains(pre.next.val)) {
                pre.next = pre.next.next;
            } else {
                pre = pre.next;
            }
        }
        return dummy.next;
    }
}