text: # Time:  O(n^2)
  # Space: O(1)
  
  class Solution(object):
      # @return a list of integers
      def getRow(self, rowIndex):
          result = [0] * (rowIndex + 1)
          for i in xrange(rowIndex + 1):
              old = result[0] = 1
              for j in xrange(1, i + 1):
                  old, result[j] = result[j], old + result[j]
          return result
  
      def getRow2(self, rowIndex):
          """
          :type rowIndex: int
          :rtype: List[int]
          """
          row = [1]
          for _ in range(rowIndex):
              row = [x + y for x, y in zip([0] + row, row + [0])]
          return row
  
      def getRow3(self, rowIndex):
          """
          :type rowIndex: int
          :rtype: List[int]
          """
          if rowIndex == 0: return [1]
          res = [1, 1]
  
          def add(nums):
              res = nums[:1]
              for i, j in enumerate(nums):
                  if i < len(nums) - 1:
                      res += [nums[i] + nums[i + 1]]
              res += nums[:1]
              return res
  
          while res[1] < rowIndex:
              res = add(res)
          return res
  
  
  # Time:  O(n^2)
  # Space: O(n)
  class Solution2(object):
      # @return a list of integers
      def getRow(self, rowIndex):
          result = [1]
          for i in range(1, rowIndex + 1):
              result = [1] + [result[j - 1] + result[j] for j in xrange(1, i)] + [1]
          return result
  
  
  