python 编写排列组合

python在编写排列组合是会用到  itertools 模块

排列 

import itertools
mylist = list(itertools.permutations(['A','B','C','D'],4))  # 全排列
print(mylist)
mylist1 = list(itertools.permutations(['A','B','C','D'],3))  # 4个里面选3个排列
print(mylist1)

#5!=1*2*3*4*5
#0!=1
#M个选N个   M！/(M-N)！
#4  1    4!/3!=4
#4 2  4!/2！=3*4=12
#4 3  4！/1！=24

组合

import itertools
mylist = list(itertools.combinations(['A','B','C','D'],4))  # 组合
print(mylist)
mylist1 = list(itertools.combinations(['A','B','C','D'],3))  # 4个里面选3个组合
print(mylist1)

#['A','B','C','D'],3) 4个取3个，无序
#M!/N!(M-N)!

可以重复的排序（类似密码）

import itertools
# product 可以重复的排序
# mylist1 = list(itertools.product("0123456789",repeat=4)) 参数表示可以重复的从前面的0到9里面取出4个数字来
# print(mylist1)
mylist=(["".join(x) for x in itertools.product("0123456789",repeat=4) ])
print(mylist)
print(len(mylist))

利用生成器可以跌代的生产密码，节约内存

#百度云，输入密码   _  _  _  _
import itertools
# product 可以重复的排序
mylist=("".join(x) for x in itertools.product("0123456789",repeat=4))
print(next(mylist))
print(next(mylist))
print(next(mylist))
print(next(mylist))