AtCoder Regular Contest 151
B
A < AP
AtCoder
⌀ 1333
原题
← AC →
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Problem Statement

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You are given a permutation $P = (P_1, P_2, \ldots, P_N)$ of $(1, 2, \ldots, N)$.

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Print the number of integer sequences $A = (A_1, A_2, \ldots, A_N)$ of length $N$ that satisfy both of the conditions below, modulo $998244353$.

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  • $1 \leq A_i \leq M$ for every $i = 1, 2, \ldots, N$.
  • The integer sequence $A$ is lexicographically smaller than the integer sequence $(A_{P_1}, A_{P_2}, \ldots, A_{P_N})$.
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What is lexicographical order? An integer sequence $X = (X_1,X_2,\ldots,X_N)$ is ** lexicographically smaller** than an integer sequence $Y = (Y_1,Y_2,\ldots,Y_N)$ when there is an integer $1 \leq i \leq N$ that satisfies both of the conditions below. For all integers $j$ ($1 \leq j \leq i-1$), $X_j=Y_j$. $X_i < Y_i$

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Constraints

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  • $1 \leq N \leq 2 \times 10^5$
  • $1 \leq M \leq 10^9$
  • $1 \leq P_i \leq N$
  • $i \neq j \implies P_i \neq P_j$
  • All values in the input 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 M
P_1 P_2 \ldots P_N

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Output

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Print the number of integer sequences $A$ of length $N$ that satisfy both of the conditions in the Problem Statement, modulo $998244353$.

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样例

Input #1
4 2
4 1 3 2
Output #1
6
Six integer sequences $A$ satisfy both of the conditions: $(1, 1, 1, 2)$, $(1, 1, 2, 2)$, $(1, 2, 1, 2)$, $(1, 2, 2, 2)$, $(2, 1, 1, 2)$, and $(2, 1, 2, 2)$. For instance, when $A = (1, 1, 1, 2)$, we have $(A_{P_1}, A_{P_2}, A_{P_3}, A_{P_4}) = (2, 1, 1, 1)$, which is lexicographically larger than $A$.
Input #2
1 1
1
Output #2
0
Input #3
20 100000
11 15 3 20 17 6 1 9 5 19 10 16 7 8 12 2 18 14 4 13
Output #3
55365742
题目信息
题号
arc151_b
时间限制
2 s
内存限制
1024 MB

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