leetcode-817-Linked-List-Components

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描述

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:

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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:

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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.

分析

在集合 G 中的属于同一个连通点，需要求链表中有多少个连通图，遍历一次链表就够了，只需要计算连通图之间的边界的个数。

解决方案1(Java)

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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public int numComponents(ListNode head, int[] G) {
        Set<Integer> Gset = new HashSet();
        for (int item: G) {
            Gset.add(item);
        }
        
        ListNode current = head;
        int result = 0;
        while(current != null) {
            if (Gset.contains(current.val) && (current.next == null || !Gset.contains(current.next.val))) {
                result++;
            }
            current = current.next;
        }
        return result;
    }
}

题目来源