817 Linked List Components

1. Question

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 inG, where two values are connected if they appear consecutively in the linked list.
Example 1:
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Input:
2
3
head: 0->1->2->3
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G = [0, 1, 3]
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Output: 2
7
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Explanation:
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0 and 1 are connected, so [0, 1] and [3] are the two connected components.
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Example 2:
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Input:
2
head: 0->1->2->3->4
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G = [0, 3, 1, 4]
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Output: 2
6
7
Explanation:
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0 and 1 are connected, 3 and 4 are connected, so [0, 1] and [3, 4] are the two connected components.
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Note:
  • If Nis 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.
  • Gis a subset of all values in the linked list.

2. Implementation

(1) HashSet
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/**
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* Definition for singly-linked list.
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* public class ListNode {
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* int val;
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* ListNode next;
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* ListNode(int x) { val = x; }
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* }
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*/
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class Solution {
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public int numComponents(ListNode head, int[] G) {
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Set<Integer> set = new HashSet();
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for (int node : G) {
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set.add(node);
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}
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int res = 0;
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while (head != null) {
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if (set.contains(head.val) && (head.next == null || !set.contains(head.next.val))) {
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++res;
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}
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head = head.next;
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}
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return res;
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}
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}
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3. Time & Space Complexity

HashSet: 时间复杂度O(n), 空间复杂度O(n)