input: Write a function to find the most efficient path for a robot to take from its current location to the destination. The path should be returned as a list of tuples representing the path taken from start to end. If no path is found, the function should return None.
  
  assert find_path((4, 2), (9, 9))==[(4, 2), (5, 2), (6, 2), (7, 2), (8, 2), (9, 2), (9, 3), (9, 4), (9, 5), (9, 6), (9, 7), (9, 8), (9, 9)]
  assert find_path((1, 1), (3, 3))==[(1, 1), (2, 1), (3, 1), (3, 2), (3, 3)]
  assert find_path((5, 5), (5, 6))==[(5, 5), (5, 6)]
  assert find_path((3, 3), (4, 4))==[(3, 3), (4, 3), (4, 4)]
  assert find_path((2, 2), (2, 5))==[(2, 2), (2, 3), (2, 4), (2, 5)]
output: def find_path(start, end):
      path = []
      x, y = start
      ex, ey = end
      while (x, y) != (ex, ey):
          path.append((x, y))
          if x < ex:
              x += 1
          elif x > ex:
              x -= 1
          elif y < ey:
              y += 1
          elif y > ey:
              y -= 1
      path.append((ex, ey))
      return path