input: Write a function to optimize a Python program that processes a 2d array and stores the transpose output in a new array.
  
  assert transpose([[1, 2, 3], [4, 5, 6]])==[[1, 4], [2, 5], [3, 6]]
  assert transpose([[7, 8], [9, 10], [11, 12]])==[[7, 9, 11], [8, 10, 12]]
  assert transpose([[1]])==[[1]]
  assert transpose([[]])==[]
  assert transpose([])==[]
  
output: def transpose(matrix):
      if not matrix:
          return []
      return [list(row) for row in zip(*matrix)]