817. Linked List Components

Problem:

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.

思路：

Solution (C++):

int numComponents(ListNode* head, vector<int>& G) {
    unordered_set<int> set_G(G.begin(), G.end());
    int res = 0;
    while (head) {
        if (set_G.count(head->val) && (!(head->next) || !set_G.count(head->next->val)))  ++ res;
        head = head->next;
    }
    return res;
}

性能：

Runtime: 44 ms  Memory Usage: 12.5 MB

思路：

Solution (C++):

性能：

Runtime: ms  Memory Usage: MB