118. 杨辉三角

class Solution:
    def generate(self, numRows):
        """
        :type numRows: int
        :rtype: List[List[int]]
        """
        ans = []
        for i in range(numRows):
            temp = [1]*(i+1)
            ans.append(temp)
            for j in range(1,i):
                ans[i][j] = ans[i-1][j-1]+ans[i-1][j]
        return ans