LeetCode Pascal's Triangle && Pascal's Triangle II Python

Pascal's Triangle

Given numRows, generate the first numRows of Pascal's triangle.

For example, given numRows = 5,
Return

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

class Solution:
    # @return a list of lists of integers

    def generate(self, numRows):
        def g(ls):
            res = [1]
            left = 1
            for i in range(1,len(ls)):
                res.append(left+ls[i])
                left = ls[i]
            res.append(1)
            return res

        res = []
        if numRows < 3:
            if numRows == 0:
                return res
            for i in range(1,numRows+1):
                res.append([1]*i)
        else:
            res.append([1])
            res.append([1,1])

            for i in range(2,numRows):
                res.append(g(res[i-1]))
        return res
        

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:
    # @return a list of integers
    def getRow(self, rowIndex):
        def g(ls):
            res = [1]
            left = 1
            for i in range(1,len(ls)):
                res.append(left+ls[i])
                left = ls[i]
            res.append(1)
            return res

        res = []
        if rowIndex< 2:
            res = [1]*(rowIndex+1)
        else:
            res.append([1,1])
            for i in range(rowIndex):
                res = (g(res))
        return res