NOMURA プログラミングコンテスト 2021 (AtCoder Regular Contest 121)
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Problem Statement
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Given is a tree with $N$ vertices numbered $1$ through $N$.
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The $i$-th edge connects Vertices $a_i$ and $b_i$.
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Snuke will label each vertex with 0 or 1 and each edge with AND or OR. Among the $2^{2N-1}$ ways to label the vertices and edges, find the number of ways that satisfy the following condition, modulo $998244353$.
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Condition: There exists a sequence of $N-1$ operations ending up with one vertex labeled 1, where each operation consists of the steps below.
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- Choose one edge and contract it. Here, let
$x$and$y$be the labels of the erased vertices and$\mathrm{op}$be the label of the erased edge. - If
$\mathrm{op}$isAND, label the new vertex with$\mathrm{AND}(x,y)$; if$\mathrm{op}$isOR, label the new vertex with$\mathrm{OR}(x,y)$.
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Note
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- The operation
$\mathrm{AND}$is defined as follows:$\mathrm{AND}(0,0)=(0,1)=(1,0)=0,\mathrm{AND}(1,1)=1$. - The operation
$\mathrm{OR}$is defined as follows:$\mathrm{OR}(1,1)=(0,1)=(1,0)=1,\mathrm{OR}(0,0)=0$. - When contracting the edge connecting Vertex
$s$and Vertex$t$, we merge the two vertices while removing that edge. After the contraction, there is an edge connecting the new vertex and vertex$u$if and only if there was an edge connecting$s$and$u$or connecting$t$and$u$before the contraction.
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Constraints
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- All values in input are integers.
$2 \leq N \leq 10^{5}$$1 \leq a_i, b_i \leq N$- The given graph is a tree.
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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 number of ways to label the tree that satisfy the condition in Problem Statement, modulo $998244353$.
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样例
Input #1
2
1 2
Output #1
4
Input #2
20
7 3
20 18
16 12
7 2
10 5
18 16
16 3
4 11
7 15
8 1
6 1
12 13
15 5
19 17
7 1
9 8
7 17
16 14
11 7
Output #2
283374562
- Remember to print the count modulo $998244353$.
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。