AtCoder Grand Contest 030
D
Inversion Sum
AtCoder
⌀ 2712
原题
← CE →
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Problem Statement

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You are given an integer sequence of length $N$: $A_1,A_2,...,A_N$. Let us perform $Q$ operations in order. The $i$-th operation is described by two integers $X_i$ and $Y_i$. In this operation, we will choose one of the following two actions and perform it:

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  • Swap the values of $A_{X_i}$ and $A_{Y_i}$
  • Do nothing
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There are $2^Q$ ways to perform these operations. Find the sum of the inversion numbers of the final sequences for all of these ways to perform operations, modulo $10^9+7$.

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Here, the inversion number of a sequence $P_1,P_2,...,P_M$ is the number of pairs of integers $(i,j)$ such that $1\leq i < j\leq M$ and $P_i > P_j$.

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Constraints

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  • $1 \leq N \leq 3000$
  • $0 \leq Q \leq 3000$
  • $0 \leq A_i \leq 10^9(1\leq i\leq N)$
  • $1 \leq X_i,Y_i \leq N(1\leq i\leq Q)$
  • $X_i\neq Y_i(1\leq i\leq Q)$
  • 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 Q
A_1
:
A_N
X_1 Y_1
:
X_Q Y_Q

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Output

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Print the sum of the inversion numbers of the final sequences, modulo $10^9+7$.

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样例

Input #1
3 2
1
2
3
1 2
1 3
Output #1
6
There are four ways to perform operations, as follows: - Do nothing, both in the first and second operations. The final sequence would be $1,2,3$, with the inversion number of $0$. - Do nothing in the first operation, then perform the swap in the second. The final sequence would be $3,2,1$, with the inversion number of $3$. - Perform the swap in the first operation, then do nothing in the second. The final sequence would be $2,1,3$, with the inversion number of $1$. - Perform the swap, both in the first and second operations. The final sequence would be $3,1,2$, with the inversion number of $2$. The sum of these inversion numbers, $0+3+1+2=6$, should be printed.
Input #2
5 3
3
2
3
1
4
1 5
2 3
4 2
Output #2
36
Input #3
9 5
3
1
4
1
5
9
2
6
5
3 5
8 9
7 9
3 2
3 8
Output #3
425
题目信息
题号
agc030_d
时间限制
3 s
内存限制
1024 MB

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