动态规划：货币组合

一共有1,2,5，10元的货币，要组合成x元

from copy import copy
f = open('台阶.txt', 'w', encoding='utf-8')

def func(num=0, ls=[]):
    ls.append(num)
    if sum(ls) > 20:
        return
    if sum(ls) == 20:
        print(ls[1:], file=f)
        return

    for i in [1, 2, 5, 10]:
        func(i, copy(ls))

func()