AtCoder Regular Contest 195 (Div. 2)
E
Random Tree Distance
AtCoder
⌀ 2734
原题
← D→
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Problem Statement

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There is an integer sequence $A = (A_2,A_3,\ldots,A_N)$. Also, for an integer sequence $P=(P_2, P_3, \ldots ,P_N)$ where $1 \leq P_i \leq i-1$ for each $i$ $(2 \leq i \leq N)$, define the weighted tree $T(P)$ with $N$ vertices, rooted at vertex $1$, as follows:

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  • A rooted tree where, for each $i$ $(2 \leq i \leq N)$, the parent of $i$ is $P_i$, and the weight of the edge between $i$ and $P_i$ is $A_i$.
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You are given $Q$ queries. Process them in order. The $i$-th query is as follows:

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  • You are given integers $u_i$ and $v_i$, each between $1$ and $N$. For each of the possible $(N-1)!$ sequences $P$, take the tree $T(P)$ and consider the distance between vertices $u_i$ and $v_i$ in this tree. Output the sum, modulo $998244353$, of these distances over all $T(P)$. Here, the distance between two vertices $u_i$ and $v_i$ is the sum of the weights of the edges on the unique path (not visiting the same vertex more than once) that connects them.
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Constraints

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  • $2 \leq N \leq 2 \times 10^5$
  • $1 \leq Q \leq 2 \times 10^5$
  • $1 \leq A_i \leq 10^9$
  • $1 \leq u_i < v_i \leq N$
  • All input values are integers.
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Input

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

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N Q
A_2 A_3 \ldots A_N
u_1 v_1
u_2 v_2
\vdots
u_Q v_Q

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Output

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Print $Q$ lines. The $i$-th line should contain the answer to the $i$-th query.

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样例

Input #1
3 2
1 1
1 2
1 3
Output #1
2
3
- If $P = (1,1)$, then in the tree $T(P)$, the distance between vertices $1$ and $2$ is $1$, and the distance between vertices $1$ and $3$ is $1$. - If $P = (1,2)$, then in the tree $T(P)$, the distance between vertices $1$ and $2$ is $1$, and the distance between vertices $1$ and $3$ is $2$. Therefore, the total distance between vertices $1$ and $2$ over all $T(P)$ is $2$, and the total distance between vertices $1$ and $3$ over all $T(P)$ is $3$.
Input #2
2 1
100
1 2
Output #2
100
Input #3
9 6
765689282 93267307 563699854 951829154 801512848 389123318 924504746 596035433
3 8
2 5
5 8
2 9
8 9
5 7
Output #3
55973424
496202632
903509579
343265517
550981449
68482696
Remember to take the sum modulo $998244353$.
题目信息
题号
arc195_e
时间限制
2 s
内存限制
1024 MB

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