817

817. Linked List Components (Medium)

We are given head, the head node of a linked list containing unique integer values.

We are also given the list G, a subset of the values in the linked list.

Return the number of connected components in G, where two values are connected if they appear consecutively in the linked list.

Example 1:

Input: 
head: 0->1->2->3
G = [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
G = [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.

Note:

• If N is the length of the linked list given by head, 1 <= N <= 10000.
• The value of each node in the linked list will be in the range [0, N - 1].
• 1 <= G.length <= 10000.
• G is a subset of all values in the linked list.

Companies:
Google

Related Topics:
Linked List

Solution 1.

// OJ: https://leetcode.com/problems/linked-list-components/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(N)
class Solution {
public:
    int numComponents(ListNode* head, vector<int>& G) {
        unordered_set<int> s(G.begin(), G.end());
        int ans = 0;
        while (true) {
            while (head && s.find(head->val) == s.end()) head = head->next;
            if (!head) break;
            ++ans;
            while (head && s.find(head->val) != s.end()) head = head->next;
        }
        return ans;
    }
};