input: Write a python function to calculate the minimum, maximum, and median temperatures from a given comma-separated string of temperatures.
  assert calculate_temperatures('82.0, 84.3, 69.6, 78.2') == (69.6, 84.3, 80.1)
  assert calculate_temperatures('60.0, 70.0, 80.0, 90.0, 100.0') == (60.0, 100.0, 80.0)
  assert calculate_temperatures('50.5, 60.5, 70.5') == (50.5, 70.5, 60.5)
output: def calculate_temperatures(temp_str):
      temps = list(map(float, temp_str.split(', ')))
      temps.sort()
      n = len(temps)
      min_temp = temps[0]
      max_temp = temps[-1]
      if n % 2 == 0:
          median_temp = (temps[n // 2 - 1] + temps[n // 2]) / 2
      else:
          median_temp = temps[n // 2]
      return (min_temp, max_temp, median_temp)