求排列组合数

perm_comb.py

def combcount(n,r):
    f = lambda n,r:n*f(n-1,r) if n>r else 1
    return f(n,n-r)/f(r,0)
def permcount(n,r):
    f = lambda n,r:n*f(n-1,r) if n>r else 1
    return f(n,n-r)
    
    
# 附带使用python的itertools求全排列、全组合函数
import itertools as it
list(it.permutations([1,2,3,4,5,6],4))
list(it.combinations([1,2,3,4,5,6],4))