def combinations(list_of_items):
"""
nPr = n! / (n_1! * n_2! * ... * n_k!)
nPr(['s','t','a','t','i','s','t','i','c','s']) == 50400
:param list_of_items:
:return: number of different combinations
"""
numerator = factorial(len(list_of_items)) # n!
char_counts = {}
for item in list_of_items:
char_counts[item] = list_of_items.count(item)
denominator = 1
for count in char_counts:
denominator *= factorial(
char_counts[count]) # n_1! * n_2! * ... * n_k!
return numerator // denominator
def test_large_factorial(self): result = problem20.factorial(100) self.assertEqual(result / int(1e155), 933L)
def test_large_factorial(self):
result = problem20.factorial(100)
self.assertEqual(result / int(1e155), 933L)
def test_small_factorial(self): result = problem20.factorial(10) self.assertEqual(result, 3628800)
def test_small_factorial(self):
result = problem20.factorial(10)
self.assertEqual(result, 3628800)
