import itertools  

排列: 4个数内选2个

>>> print list(itertools.permutations([1,2,3,4],2))

[(1, 2), (1, 3), (1, 4), (2, 1), (2, 3), (2, 4), (3, 1), (3, 2), (3, 4), (4, 1), (4, 2), (4, 3)]

组合：4个数内选2个：

>>> print list(itertools.combinations([1,2,3,4],2))

[(1, 2), (1, 3), (1, 4), (2, 3), (2, 4), (3, 4)]

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ABCDE 5个数的排列(去掉重复):

>>>len(set(list(itertools.permutations(['A','B','C','D','E'],5))))

120

AABCD 5个数不同的排列(去掉重复):

>>>len(set(list(itertools.permutations(['A','A','B','C','D'],5))))

60

AABBC(去掉重复):

>>> len(set(list(itertools.permutations(['A','A','B','B','C'],5))))

30

AAABC(去掉重复):

>>> len(set(list(itertools.permutations(['A','A','A','B','C'],5))))

20

AAABB(去掉重复):

>>> len(set(list(itertools.permutations(['A','A','A','B','B'],5))))

10

AAAAB(去掉重复):

>>> len(set(list(itertools.permutations(['A','A','A','A','B'],5))))

5

import math

//求阶乘

math.factorial(3)

//求排列数 : n个数选x个

def P(n,x):

	return math.factorial(n)/math.factorial(n-x)

//求组合数 : n个数选x个

def C(n,x):

	return P(n,x) / math.factorial(x)

一手牌满堂红的概率:(5张牌，3张点相同，另2张点数相同)

P(13,2) * C(4,3) * C(4,2) / C(13*4,5) = 0.0014405762304921968