Geometric Series Modulo — Solution & Editorial
Closed form A(qN−1)/(q−1) using the modular inverse of q−1 — but q = 1 needs the special case A·N.
Complexity: O(log N)
Watch out: q = 1 divides by zero in the closed form — handle it as A·N separately.
Closed form A(qN−1)/(q−1) using the modular inverse of q−1 — but q = 1 needs the special case A·N.
Complexity: O(log N)
Watch out: q = 1 divides by zero in the closed form — handle it as A·N separately.