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

class NonPositiveArgumentError(Exception):
    pass

class WrongArgumentsOrderError(Exception):
    pass

def get_combination(k: int, n: int) -> int:
    if k <= 0:
        raise NonPositiveArgumentError("k must be positive.")
    if n <= 0:
        raise NonPositiveArgumentError("n must be positive.")
    if n < k:
        raise WrongArgumentsOrderError("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 *


@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(9, 15), 5005.0)
        test.assert_equals(get_combination(45, 201), 1.773741968572955e+45)
    @test.it("Exceptions")
    def exceptions():
        test.expect_error('', lambda:get_combination(7, 5), exception=WrongArgumentsOrderError)
        test.expect_error('', lambda:get_combination(-1, 5), exception=NonPositiveArgumentError)
        test.expect_error('', lambda:get_combination(1, -5), exception=NonPositiveArgumentError)
    View Run Output
  • Code
    • from math import factorial
    • class NonPositiveArgumentError(Exception):
    • pass
    • class WrongArgumentsOrderError(Exception):
    • pass
    • def get_combination(k: int, n: int) -> int:
    • if k <= 0 or n <= 0:
    • return "n and k must be positive."
    • if k <= 0:
    • raise NonPositiveArgumentError("k must be positive.")
    • if n <= 0:
    • raise NonPositiveArgumentError("n must be positive.")
    • if n < k:
    • return "n must be greater than or equal to k."
    • return factorial(n) / (factorial(n-k)*factorial(k))
    • raise WrongArgumentsOrderError("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
    • from solution import *
    • @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)
    • test.assert_equals(get_combination(45, 201), 1.773741968572955e+45)
    • @test.it("Exceptions")
    • def exceptions():
    • test.expect_error('', lambda:get_combination(7, 5), exception=WrongArgumentsOrderError)
    • test.expect_error('', lambda:get_combination(-1, 5), exception=NonPositiveArgumentError)
    • test.expect_error('', lambda:get_combination(1, -5), exception=NonPositiveArgumentError)