AtCoder Beginner Contest 447
F
蜈蚣图
Centipede Graph
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⌀ 1480
原题
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蜈蚣图AI (CI翻译)

Problem Statement

题目描述

AI (CI翻译)

You are given a tree $T$ with $N$ vertices numbered $1$ to $N$. The $i$-th edge connects vertices $A_i$ and $B_i$.

给定一棵有 $N$ 个顶点的树 $T$,顶点编号为 $1$ 至 $N$。第 $i$ 条边连接顶点 $A_i$ 和 $B_i$。AI (CI翻译)

For a positive integer $k$, define a "centipede graph of length $k$" as a graph with $3k$ vertices obtained by the following procedure:

对于正整数 $k$,将一个含有 $3k$ 个顶点的图称为“长度为 $k$ 的蜈蚣图”,其构造过程如下:AI (CI翻译)

  • Prepare a path graph with $k$ vertices.
  • For each vertex $v$ of the path graph, add two new vertices adjacent only to $v$.
  • 准备一个含有 $k$ 个顶点的路径图。
  • 对于路径图中的每个顶点 $v$,添加两个仅与 $v$ 相邻的新顶点。
AI (CI翻译)

For example, a centipede graph of length $4$ is as shown in the figure below.

例如,长度为 $4$ 的蜈蚣图如下图所示。AI (CI翻译)

image

imageAI (CI翻译)

Find the maximum $x$ such that a "centipede graph of length $x$" is contained as a subgraph of tree $T$.

求最大的 $x$,使得“长度为 $x$ 的蜈蚣图”是树 $T$ 的子图。AI (CI翻译)

$Q$ test cases are given; solve each of them.

共有 $Q$ 组测试用例,请分别求出每组的答案。AI (CI翻译)

Constraints

约束条件

AI (CI翻译)
  • $1 \le Q$
  • $3 \le N \le 2 \times 10^5$
  • $1 \le A_i, B_i \le N$
  • The given graph is a tree.
  • The sum of $N$ over all test cases is at most $2 \times 10^5$.
  • All input values are integers.
  • $1 \le Q$
  • $3 \le N \le 2 \times 10^5$
  • $1 \le A_i, B_i \le N$
  • 给定的图是一棵树。
  • 所有测试用例的 $N$ 之和不超过 $2 \times 10^5$。
  • 所有输入值均为整数。
AI (CI翻译)

Input

输入格式

AI (CI翻译)

The input is given from Standard Input in the following format:

输入从标准输入按以下格式给出:AI (CI翻译)

Q
\text{case}_1
\text{case}_2
\vdots
\text{case}_Q

Q
\text{case}_1
\text{case}_2
\vdots
\text{case}_Q
AI (CI翻译)

Each test case is given in the following format:

每组测试用例的输入格式如下:AI (CI翻译)

N
A_1 B_1
A_2 B_2
\vdots
A_{N-1} B_{N-1}

N
A_1 B_1
A_2 B_2
\vdots
A_{N-1} B_{N-1}
AI (CI翻译)

Output

输出格式

AI (CI翻译)

Output $Q$ lines.

输出 $Q$ 行。AI (CI翻译)

The $i$-th line should contain the answer for the $i$-th test case.

第 $i$ 行应包含第 $i$ 组测试用例的答案。AI (CI翻译)

样例

Input #1
3
8
1 3
2 4
2 5
2 6
3 5
4 7
5 8
5
1 5
1 2
1 3
3 4
15
13 3
4 13
11 1
14 9
9 13
13 6
1 10
7 9
13 2
10 5
3 12
15 13
9 10
12 8
Output #1
2
1
3
For the first test case, the graph consisting of the six vertices $2,3,4,5,6,8$ forms a "centipede graph of length $2$". No centipede graph of length $3$ or more is contained as a subgraph, so the answer is $2$. Thus, output $2$.
题目信息
题号
abc447_f
时间限制
2 s
内存限制
1024 MB

题面与样例版权归 AtCoder 及出题人所有;中文翻译由 AI 生成(gpt-6.1-sol),如有出入请以原文为准。