input: Write a function to predict the next day's forecast temperature using the exponential smoothing algorithm given the past three day's forecast temperatures. The function should take a list of three temperatures as input and return the predicted temperature for the next day. If the input list is empty, the function should return 0.0.
  assert predict_temperature([21, 22, 20])==21.5
  assert predict_temperature([15, 17, 16])==16.5
  assert predict_temperature([25, 26, 24])==24.5
  assert predict_temperature([])==0.0
output: def predict_temperature(temps):
      if not temps:
          return 0.0
      alpha = 0.5
      return alpha * temps[-1] + (1 - alpha) * (alpha * temps[-2] + (1 - alpha) * temps[-3])