AtCoder Regular Contest 116
E
Spread of Information
AtCoder
⌀ 2236
原题
← DF →
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Problem Statement

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Takahashi Kingdom has $N$ towns, called Town $1$ through $N$. There are $N-1$ roads in this kingdom. The $i$-th road connects Town $u_i$ and Town $v_i$ bidirectionally. For any two towns $a$ and $b$, it is possible to get from Town $a$ to Town $b$ by traversing some roads.

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Takahashi, the king, wants to spread some information all over the kingdom. Since he is busy, he can directly transmit this information to at most $K$ towns.

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Assume that Takahashi finishes transmitting the information at time $0$. Then, for each $t = 1, 2, 3, \cdots$, the following happens:

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  • For towns $a$ and $b$ directly connected by a road, if $a$ has already received the information at time $t - 0.5$ but $b$ has not, $b$ receives it at time $t$.
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Takahashi wants to choose the $K$ towns to transmit the information to minimize the time taken until every town receives it. Find the minimum time this takes.

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Constraints

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  • All values in input are integers.
  • $1 \leq K < N \leq 2 \times 10^5$
  • $1 \leq u_i, v_i \leq N$
  • For any two towns $a$ and $b$, it is possible to get from Town $a$ to Town $b$ by traversing some roads.
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Input

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Input is given from Standard Input in the following format:

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N K
u_1 v_1
u_2 v_2
\vdots
u_{N-1} v_{N-1}

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Output

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Print the answer.

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样例

Input #1
5 2
1 2
2 3
3 4
4 5
Output #1
1
If Takahashi directly transmits the information to Town $2$ and $4$, Town $1, 2, 3, 4, 5$ receives it at time $1, 0, 1, 0, 1$, respectively. In this case, the information is spread all over the kingdom at time $1$. We can prove that this is the earliest possible time.
Input #2
5 1
1 2
1 3
1 4
5 4
Output #2
2
Input #3
20 3
2 15
6 5
12 1
7 9
17 2
15 5
2 4
17 16
12 2
8 17
17 19
18 11
20 8
20 3
13 9
11 10
11 20
14 8
11 7
Output #3
3
题目信息
题号
arc116_e
时间限制
3 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(CI 管线),如有出入请以原文为准。