Codeforces Round 838 (Div. 2)
E
Tree Sum
Codeforces
2600
原题
← DF →
翻译中…

Let us call an edge-weighted tree with $n$ vertices numbered from $1$ to $n$ good if the weight of each edge is either $1$ or $-1$ and for each vertex $i$, the product of the edge weights of all edges having $i$ as one endpoint is $-1$.

翻译中…

You are given a positive integer $n$. There are $n^{n-2} \cdot 2^{n-1}$ distinct$^\dagger$ edge-weighted trees with $n$ vertices numbered from $1$ to $n$ such that each edge is either $1$ or $-1$. Your task is to find the sum of $d(1,n)^\ddagger$ of all such trees that are good. Since the answer can be quite large, you only need to find it modulo $998\,244\,353$.

翻译中…

$^\dagger$ Two trees are considered to be distinct if either:

翻译中…
  • there exists two vertices such that there is an edge between them in one of the trees, and not in the other.
  • there exists two vertices such that there is an edge between them in both trees but the weight of the edge between them in one tree is different from the one in the other tree.
翻译中…

Note that by Cayley's formula, the number of trees on $n$ labeled vertices is $n^{n-2}$. Since we have $n-1$ edges, there are $2^{n-1}$ possible assignment of weights(weight can either be $1$ or $-1$). That is why total number of distinct edge-weighted tree is $n^{n-2} \cdot 2^{n-1}$.

翻译中…

$^\ddagger$ $d(u,v)$ denotes the sum of the weight of all edges on the unique simple path from $u$ to $v$.

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Input

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The first and only line of input contains a single integer $n$ ($1 \leq n \leq 5 \cdot 10^5$).

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Output

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The only line of output should contain a single integer, the required answer, modulo $998\,244\,353$.

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Note

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In the first test case, there is only $1$ distinct good tree. The value of $d(1,2)$ for that tree is $-1$, which is $998\,244\,352$ under modulo $998\,244\,353$.

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In the second test case, the value of $d(1,1)$ for any tree is $0$, so the answer is $0$.

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In the third test case, there are $16$ distinct good trees. The value of $d(1,4)$ is:

翻译中…
  • $-2$ for $2$ trees;
  • $-1$ for $8$ trees;
  • $0$ for $4$ trees;
  • $1$ for $2$ trees.
翻译中…

The sum of $d(1,4)$ over all trees is $2 \cdot (-2) + 8 \cdot (-1) + 4 \cdot (0) + 2 \cdot (1) = -10$, which is $998\,244\,343$ under modulo $998\,244\,353$.

翻译中…

样例

Input #1
2
Output #1
998244352
InputCopy OutputCopy
Input #2
1
Output #2
0
InputCopy OutputCopy
Input #3
4
Output #3
998244343
InputCopy OutputCopy
Input #4
10
Output #4
948359297
InputCopy OutputCopy
Input #5
43434
Output #5
86232114
InputCopy OutputCopy
题目信息
题号
1762E
时间限制
3 s
内存限制
256 MB
标签
组合数学
数学
树

题面与样例版权归 Codeforces 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。