817. Linked List Components

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817. Linked List Components

题目描述

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.

题目大意

求链表中的连通分量个数。

解题思路

当 g 中不包含链表中的节点时，则代表一个连通分量。
移除已检索过的节点值，减少 contains 的复杂度。

代码

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class Solution {
    func numComponents(_ head: ListNode?, _ G: [Int]) -> Int {
        var pre = head
        var g = Set(G)
        var ans = 0
        var flag = false
        while let node = pre {
            if !g.contains(node.val) {
                ans += flag ? 1 : 0
                flag = false
            }else {
                g.remove(node.val)
                flag = true
            }
            pre = pre?.next
        }
        return flag ? ans + 1 : ans
    }
}
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