CodingHardcod-g492

Subject Advanced dpLevel Senior–Staff~30 minCommon in Algorithms & data structures interviewsIndustries Software development

Question

Count the number of surjective (onto) functions from a set of size `n` to a set of size `m`, i.e. functions that hit every one of the m targets at least once. Return the count modulo 1_000_000_007. If m > n the answer is 0; n,m can be up to a few thousand.

Implement

count_surjections(n: int, m: int) → int

Examples

in[3,2]out6

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.