关于CodeChef题目BROCLK中模逆元表述的疑问

Great question—this is a super common point of confusion when diving into programming competition problem statements, especially number theory-focused ones like CodeChef's BROCLK.

Let me break this down clearly:

• In competitive programming contexts (like CodeChef problems), when a statement mentions a "modular inverse of q" without explicitly restating the modulus, it always refers to a modulus that was already defined earlier in the problem statement.
• This is a standard shorthand to avoid repetitive wording—problem setters assume you’ve already noted the fixed modulus given in the problem’s setup, input constraints, or introductory formulas.

For example, many CodeChef number theory problems use common primes like 1e9+7 or 998244353 as the default modulus, but the specific one here would have been stated somewhere before that line you quoted. The problem’s guarantee that the inverse exists and is unique further confirms this: a modular inverse of q only exists if q and the modulus are coprime, which the problem has already accounted for by setting up the modulus and constraints accordingly.

If you double-check the earlier sections of the BROCLK problem (like the problem description, input rules, or prior mathematical definitions), you’ll definitely find the exact modulus being referenced here.

内容的提问来源于stack exchange，提问作者Devansh