题目：
题解：
class Solution:def generate(self, numRows: int) -> List[List[int]]:ret = list()for i in range(numRows):row = list()for j in range(0, i + 1):if j == 0 or j == i:row.append(1)else:row.append(ret[i - 1][j] + ret[i - 1][j - 1])ret.append(row)return ret
