input: from typing import List
  
  def pascal_triangle(n: int) -> List[List[int]]:
      """
      Prints out Pascal's triangle for a given number of rows.
      
      >>> pascal_triangle(5)
      [[1], [1, 1], [1, 2, 1], [1, 3, 3, 1], [1, 4, 6, 4, 1]]
      """
      if n < 1:
          return []
      trow = [1]
      triangle = []
      for x in range(n):
          triangle.append(trow)
          trow = [l + r for l, r in zip([0] + trow, trow + [0])]
      return triangle
output:     if n < 1:
          return []
      trow = [1]
      triangle = []
      for x in range(n):
          triangle.append(trow)
          trow = [l + r for l, r in zip([0] + trow, trow + [0])]
      return triangle