Given a non-negative integer numRows, generate the first numRows of Pascal's triangle.
pascal 三角形
a[i][j] = a[i - 1][j - 1] + a[i - 1][j]
class Solution(object): def generate(self, numRows): """ :type numRows: int :rtype: List[List[int]] """ ans = [] for i in range(0, numRows, 1): sub = [] for j in range(0, i + 1, 1): if j == 0 or j == i: sub.append(1) else: sub.append(ans[i - 1][j] + ans[i - 1][j - 1]) ans.append(sub) return ans