[Python手撕]不同的二叉搜尋樹

class Solution:
    def numTrees(self, n: int) -> int:
        dp = [0]*(n+1)
        dp[0] = 1
        dp[1] = 1
        for i in range(2,n+1):
            for j in range(i):
                dp[i] += dp[j]*dp[i-1-j]
        return dp[-1]