分割統治法で階乗計算

main.py

# -*- encoding: utf-8 -*-

def each_slice_2(f, iterator):
    a = iterator.__iter__()
    for i in a:
        try:
            j = a.__next__()
        except:
            j = 0
        yield f(i, j)

def fanc(n):
    a = range(1, n-1)
    while n > 0:
        a = each_slice_2(lambda x, y: x * y if y != 0 else x, a)
        n = n // 2
    return a.__next__()

def main():
    n = int(input())
    print(fanc(n))

if __name__ == "__main__":
    main()