• + 1 comment

    Hint:-

    Here total number of possibilities are 3(3N).

    M = 109+7.
    To calculate (ab)%M and we know b can be very large(3N) .
    Using Fermat's little theorem (a(M-1))%M = 1, first we will do b=b%(M-1) and then calculate (ab)%M by using fast exponentiation.
    References :-
    1. Codechef Discussion
    2. Geeksforgeeks