Score : 1000 points
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:
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 is given from Standard Input in the following format:
N Q A_1 : A_N X_1 Y_1 : X_Q Y_Q
Print the sum of the inversion numbers of the final sequences, modulo 10^9+7.
3 2 1 2 3 1 2 1 3
6
There are four ways to perform operations, as follows:
The sum of these inversion numbers, 0+3+1+2=6, should be printed.
5 3 3 2 3 1 4 1 5 2 3 4 2
36
9 5 3 1 4 1 5 9 2 6 5 3 5 8 9 7 9 3 2 3 8
425