AtCoder Regular Contest 142
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Problem Statement
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We have a tree with $N$ vertices, numbered $1, \ldots, N$. For each $i=1,\ldots,N-1$, the $i$-th edge connects Vertex $a_i$ and Vertex $b_i$.
An operation on this tree when at most one piece is put on each vertex is defined as follows.
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- Simultaneously move every piece to one of the vertices adjacent to the one occupied by the piece.
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An operation is said to be good when the conditions below are satisfied.
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- Each edge is traversed by at most one piece.
- Each vertex will be occupied by at most one piece after the operation.
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Takahashi will put a piece on one or more vertices of his choice. Among the $2^N-1$ ways to put pieces, find the number of ones that satisfy the condition below, modulo $998244353$.
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- For every non-negative integer
$K$, the following holds. - It is possible to perform a good operation
$K$times.- Let
$S_K$be the set of vertices occupied by pieces just after$K$good operations. Then,$S_K$is unique.
- Let
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Constraints
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$2 \leq N \leq 2 \times 10^5$$1 \leq a_i \lt b_i \leq N$- The given graph is a tree.
- All values in input are integers.
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Input
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Input is given from Standard Input in the following format:
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N
a_1 b_1
\vdots
a_{N-1} b_{N-1}
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Output
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Print the answer.
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样例
Input #1
3
1 2
1 3
Output #1
2
Here are the two ways to satisfy the condition.
- Put a piece on Vertex $1$ and Vertex $2$.
- Put a piece on Vertex $1$ and Vertex $3$.
Note that he must put a piece on at least one vertex.
Input #2
7
1 2
1 3
2 4
2 5
3 6
3 7
Output #2
0
There might be no way to satisfy the condition.
Input #3
19
9 14
2 13
1 3
17 19
13 18
12 19
4 5
2 10
4 9
8 11
3 15
6 8
8 10
6 19
9 13
11 15
7 17
16 17
Output #3
100
题目信息
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。