input: Write a function to use the exponential smoothing algorithm to predict the next day's forecast temperature given the past three day's forecast temperatures. The function should take a list of three temperatures as input and return the predicted temperature. 
  
  assert predict_temperature([21, 22, 20])==21.0
  assert predict_temperature([20, 21, 22])==21.5
  assert predict_temperature([19, 20, 21])==20.5
  assert predict_temperature([22, 23, 23])==23.0
  assert predict_temperature([21, 20, 19])==19.0
output: def predict_temperature(temps):
      alpha = 0.5
      return alpha * temps[2] + (1 - alpha) * (alpha * temps[1] + (1 - alpha) * temps[0])