PU Pascal’s Triangle

[
     [1],
    [1,1],
   [1,2,1],
  [1,3,3,1],
 [1,4,6,4,1]
]

class Solution(object):
    def generate(self, numRows):
        """
        :type numRows: int
        :rtype: List[List[int]]
        """
        if numRows < 1:
            return []
        res = [[1]]
        i = 1
        while i < numRows:
            i += 1
            pre = res[-1]
            new = [1]
            for j in range(1, len(pre)):
                new.append(pre[j] + pre[j - 1])
            new.append(1)
            res.append(new)
        return res

class Solution(object):
    def generate(self, numRows):
        """
        :type numRows: int
        :rtype: List[List[int]]
        """
        if numRows < 1: return []
        res = [[1]]
        for i in range(1, numRows):
            res.append(map(lambda x, y: x + y, [0] + res[-1], res[-1] + [0]))
        return res