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Rooted by: Combination of k in n
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  • Code 
    from math import factorial

def get_combination(k: int, n: int) -> int:
    if k <= 0 or n <= 0:
        return "n and k must be positive."
    if n < k:
        return "n must be greater than or equal to k."
    return factorial(n) / (factorial(n-k)*factorial(k))
    Test Cases 
    import codewars_test as test
from solution import get_combination


@test.describe("Example")
def test_group():
    @test.it("test case")
    def test_case():
        test.assert_equals(get_combination(1, 13), 13.0)
        test.assert_equals(get_combination(7, 76), 2186189400.0)
        test.assert_equals(get_combination(7, 5), "n must be greater than or equal to k.")
        test.assert_equals(get_combination(-1, 5), "n and k must be positive.")
        test.assert_equals(get_combination(9, 15), 5005.0)
        test.assert_equals(get_combination(45, 201), 1.773741968572955e+45)
    View Run Output
  • Code
    • def get_combination(k, n):
    • def fact(x):
    • res = 1
    • for i in range(1,x+1): res*=i
    • return res
    • from math import factorial
    • def get_combination(k: int, n: int) -> int:
    • if k <= 0 or n <= 0:
    • return "n and k must be positive."
    • if n < k:
    • return "n must be greater than or equal to k."
    • return fact(n) / (fact(n-k)*fact(k))
    • return factorial(n) / (factorial(n-k)*factorial(k))