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817. Linked List Components

Description

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.

Solutions

Solution 1

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# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def numComponents(self, head: Optional[ListNode], nums: List[int]) -> int:
        ans = 0
        s = set(nums)
        while head:
            while head and head.val not in s:
                head = head.next
            ans += head is not None
            while head and head.val in s:
                head = head.next
        return ans

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/**
 * 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[] nums) {
        int ans = 0;
        Set<Integer> s = new HashSet<>();
        for (int v : nums) {
            s.add(v);
        }
        while (head != null) {
            while (head != null && !s.contains(head.val)) {
                head = head.next;
            }
            ans += head != null ? 1 : 0;
            while (head != null && s.contains(head.val)) {
                head = head.next;
            }
        }
        return ans;
    }
}

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/**
 * 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:
    int numComponents(ListNode* head, vector<int>& nums) {
        unordered_set<int> s(nums.begin(), nums.end());
        int ans = 0;
        while (head) {
            while (head && !s.count(head->val)) head = head->next;
            ans += head != nullptr;
            while (head && s.count(head->val)) head = head->next;
        }
        return ans;
    }
};

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/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func numComponents(head *ListNode, nums []int) int {
    s := map[int]bool{}
    for _, v := range nums {
        s[v] = true
    }
    ans := 0
    for head != nil {
        for head != nil && !s[head.Val] {
            head = head.Next
        }
        if head != nil {
            ans++
        }
        for head != nil && s[head.Val] {
            head = head.Next
        }
    }
    return ans
}

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