Surjective functions count
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) → intExamples
in
[3,2]out6What 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.
0:00 of about 30 min
solution.py
InputExpectedGot
[3,2]6not run yetsample