n个数中取r个数的全排列 python

a = [0 for i in range(20)]
visit = [0 for i in range(20)]
n,r = map(int,input().split())

def Print():
    for i in range(1,r+1):
        print(a[i],end=' ')
    print()


def dfs(k):
    for i in range(1,n+1):
        if visit[i] != 1:
            a[k] = i
            visit[i] = 1
            if k == r:
                Print()
            else:
                dfs(k+1)
            visit[i] = 0    


dfs(1)