Linked list components

/*
 * You are given the head of a linked list containing unique integer values and an integer array nums that is a subset of the linked list values.
 * Return the number of connected components in nums where two values are connected if they appear consecutively in the linked list.
 * Example 1:
 * Input: head = [0,1,2,3], nums = [0,1,3]
 * Output: 2
 * Explanation: 0 and 1 are connected, so [0, 1] and [3] are the two connected components.
 * Example 2:
 * Input: head = [0,1,2,3,4], nums = [0,3,1,4]
 * Output: 2
 * Explanation: 0 and 1 are connected, 3 and 4 are connected, so [0, 1] and [3, 4] are the two connected components.
 * Constraints:
 * The number of nodes in the linked list is n.
 * 1 <= n <= 104
 * 0 <= Node.val < n
 * All the values Node.val are unique.
 * 1 <= nums.length <= n
 * 0 <= nums[i] < n
 * All the values of nums are unique.
 */
impl Solution {
  pub fn num_components(head: Option<Box<ListNode>>, nums: Vec<i32>) -> i32 {
    use std::collections::HashSet;
    let set: HashSet<i32> = nums.into_iter().collect();
    let mut count = 0;
    let mut prev_in = false;
    let mut cur = &head;
    while let Some(node) = cur {
      if set.contains(&node.val) {
        if !prev_in { count += 1; }
        prev_in = true;
      } else {
        prev_in = false;
      }
      cur = &node.next;
    }
    count
  }
}