CodingHardcod-g629

Subject Combinatorial countingLevel Senior–Staff~30 minCommon in Algorithms & data structures interviewsIndustries Software development

Question

Compute the binomial coefficient C(n, r) modulo a prime p, where 0 <= r <= n <= 100000 and p is a prime up to 10^9+7. Precompute factorials and inverse factorials so multiple queries would be cheap, but for this signature just return the single value. If r < 0 or r > n, return 0.

Implement

ncr_mod_p(n: int, r: int, p: int) → int

Examples

in[5,2,1000000007]out10

What a strong answer looks like

State your approach and its time/space complexity out loud before you optimize. Handle the edge cases (empty input, duplicates, overflow), and say why you chose this over the brute force. Green tests are the floor, not the grade.

Learn the concepts

Vibe coding: describe the solution in plain language (or narrate it) and the coach grades your approach. Generating runnable code from your description is coming next.

Run or narrate your approach, then ask the coach.