817. Linked List Components

/**
817. Linked List Components
Runtime: 5 ms, faster than 90.72% of Java online submissions for Linked List Components.
Memory Usage: 39.4 MB, less than 95.74% of Java online submissions for Linked List Components.


 * 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 int numComponents(ListNode head, int[] G) {
        HashSet<Integer> setG = new HashSet<>();
        for (int i: G) setG.add(i);
        int res = 0;
        while (head != null) {
            if (setG.contains(head.val) && (head.next == null || !setG.contains(head.next.val)))
                res++;
            head = head.next;
        }
        return res;
    }
}