时间复杂度：

空间复杂度：

时间比空间重要

递归：

递归特征：

递归案例：

汉诺塔问题：

def hanoi(n,A,B,C):
    if n>0:
        hanoi(n-1,A,C,B)
        print("moving from %s to %s"%(A,C))
        hanoi(n-1,B,A,C)

hanoi(3,"a","b","c")

moving from a to c
moving from a to b
moving from c to b
moving from a to c
moving from b to a
moving from b to c
moving from a to c

汉诺塔移动次数的递推式：h(x)=2h(x)+1

原视频：https://www.bilibili.com/video/BV1uA411N7c5?p=7&spm_id_from=pageDriver&vd_source=9baef983d7bc08245d4dee5c9e676ee9