Maruo and the Sequence

sazerterus25 BUET CSE Fest 2019 Inter...
Limits 2s, 512 MB

Maruo has a sequece A = {a1,a2,}.
Let us define a function func(A,l,r) which is the minimum i such that ai is the maximum value where l<=i<=r.
Two sequences A and B are similar if they have the same length n and for every 1<=l<=r<=n , func(A,l,r) = func(B,l,r).
For any given sequence A={a1,a2,}, we define the weight of a sequence B={b1,b2,} be
∑bi, where 1<=i<=n, if the two sequences A and B are similar. Otherwise, we let the weight be equal to 0. If each element of B is chosen independently and uniform randomly between 0 and 1, find the expected weight of B.

Please note that the elements of B are real numbers between 0 and 1 inclusive, and not necessarily only 0 or 1.


The first line will contain n (the length of the sequence) 1<=n<=1000000.
The second line contains n integers (1<=ai<=n) denoting the sequence.


The expected weight will be a rational number p/q, where p and q are co-prime numbers.
Output the answer modulo 109+7 i.e. output pq-1 modulo 109+7.


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