Python排列组合实验

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