题目描述
Problem Statement
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:
- Swap the values of A_{X_i} and A_{Y_i}
- Do nothing
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.
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.
Input
Input is given from Standard Input in the following format:
N Q
A_1
:
A_N
X_1 Y_1
:
X_Q Y_Q
Output
Print the sum of the inversion numbers of the final sequences, modulo 10^9+7.
Constraints
- $1 \leq N \leq 3000$
- $0 \leq Q \leq 3000$
- $0 \leq A_i \leq 10^9(1\leq i\leq N)$
- $1 \leq X_i,Y_i \leq N(1\leq i\leq Q)$
- $X_i\neq Y_i(1\leq i\leq Q)$
- All values in input are integers.
Sample Input 1
3 2
1
2
3
1 2
1 3
Sample 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.
Sample Input 2
5 3
3
2
3
1
4
1 5
2 3
4 2
Sample Output 2
36
Sample Input 3
9 5
3
1
4
1
5
9
2
6
5
3 5
8 9
7 9
3 2
3 8
Sample Output 3
425
输入格式
见题面 Input 部分
输出格式
见题面 Output 部分