118. Pascal's Triangle

class Solution:
    def generate(self, numRows: int) -> List[List[int]]:
        res = []
        for i in range(0, numRows):
            if i == 0:
                res.append([1])
            else:
                last = res[i - 1]
                row_inner = [(last[j - 1] + last[j]) for j in range(1, len(last))]
                res.append([1] + row_inner + [1])
        return res