In [1]:

    

from operator import mul
from functools import reduce


    

In [2]:

    

def combinations_count(n, r):
    r = min(r, n - r)
    numer = reduce(mul, range(n, n - r, -1), 1)
    denom = reduce(mul, range(1, r + 1), 1)
    return numer // denom


    

In [3]:

    

print(combinations_count(4, 2))


    

    




6

In [4]:

    

print(combinations_count(4, 0))


    

    




1