递归的经典例子
1) 斐波那契数列, F(1)=1,F(2)=1, F(3)=2,F(n)=F(n-1)+F(n-2)
def fib(n):
if n < 1:
raise ValueError
elif (n == 1) or (n == 2):
return 1
else:
return fib(n - 1) + fib(n - 2)
print(fib(1)) #1
print(fib(2)) #1
print(fib(3)) #2
print(fib(4)) #3
print(fib(5)) #5
print(fib(6)) #8