119. Pascal's Triangle II

Given a non-negative index k where k ≤ 33, return the kth index row of the Pascal's triangle.

Note that the row index starts from 0.

只额外开O（k）的空间，那就开一个两行k列的数组，滚动记录上一次的结果就行

class Solution(object):
    def getRow(self, rowIndex):
        """
        :type rowIndex: int
        :rtype: List[int]
        """
        ans = [[1] * (rowIndex + 1), [1] * (rowIndex + 1)]
        for index in range(1, rowIndex + 2, 1):
            for i in range(1, index - 1, 1):
                ans[index % 2][i] = ans[(index - 1) % 2][i] + ans[(index - 1) % 2][i - 1]
        
        return ans[(rowIndex + 1) % 2]