835. Linked List Components

• Difficulty: Medium

• Topics: Linked List

• Similar Questions:

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.

Solutions:

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    int numComponents(ListNode* head, vector<int>& G) {
        unordered_set<int> nums(G.begin(), G.end());
        ListNode* cur = head;
        int ret = 0;
        bool hasNum = false;
        while (cur) {
            if (nums.count(cur->val) == 0) {
                if (hasNum) {
                    ++ret;
                    hasNum = false;
                }
                cur = cur->next;
            } else {
                hasNum = true;
                cur = cur->next;
            }
        }

        if (hasNum) {
            ++ret;
        }

        return ret;
    }
};