题目如下:

Python代码:
def numTrees(self, n):
"""
:type n: int
:rtype: int
"""
num=[0]*(n+1)
num[0]=num[1]=1
for i in range(2,n+1):
for j in range(i):
num[i] += num[j]*num[i-j-1]
return num[n]
转载于:https://www.cnblogs.com/CQUTWH/p/7201123.html