Pascal's Triangle II

Given an index k, return the kth row of the Pascal's triangle.

For example, given k = 3, Return [1,3,3,1].

Note: Could you optimize your algorithm to use only O(k) extra space?

class Solution(object):
    def getRow(self, rowIndex):
        """
        :type rowIndex: int
        :rtype: List[int]
        """
        row = [1]
        for i in range(1, rowIndex + 1):
            row = [1] + [ row[x] + row[x - 1] for x in range(1, i)] + [1]
        return row

Trick:

class Solution(object):
    def getRow(self, rowIndex):
        """
        :type rowIndex: int
        :rtype: List[int]
        """
        res = [1]
        for i in range(rowIndex):
            res[:] = map(lambda x, y: x + y, res + [0], [0] + res)
        return res