817 Linked List Components

Python

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def numComponents(self, head, G):
        """
        :type head: ListNode
        :type G: List[int]
        :rtype: int
        """
        Gset = set(G)
        cur = head
        ans = 0
        while cur:
            if cur.val in Gset and (cur.next is None or cur.next.val not in Gset):
                ans += 1
            cur = cur.next
        return ans

Java

class Solution {
    public int numComponents(ListNode head, int[] G) {
        Set<Integer> Gset = new HashSet();
        for (int x: G) Gset.add(x);

        ListNode cur = head;
        int ans = 0;

        while (cur != null) {
            if (Gset.contains(cur.val) &&
                    (cur.next == null || !Gset.contains(cur.next.val)))
                ans++;
            cur = cur.next;
        }

        return ans;
    }
}