public void cleanData(double lower, double upper) {
    // screw iterating backwards so i'm using another array
    ArrayList<Double> cleaned = new ArrayList<>();
    
    for (double temperature : temperatures) {
        if (temperature >= lower && temperature <= upper) {
            // add in same order
            cleaned.add(temperature);
        }
    }
    
    // simply overwrite old array, no removing. 
    temperatures = cleaned;
}

b)

public int longestHeatWave(double threshold)  
{ 
   // default is 0, i lazy
   int duration, max; 
 
   for (double temperature : temperatures)  { 
      // for every temperature checked that is greater than the threshold, the length of the wave increases by one
      if (temperature > threshold)  { 
         duration++;  
         if (duration > max)  { 
            // set new max if reached
            max = duration; 
         } 
      } 
      // reset duration to 0
      else  { 
         duration = 0;          
      } 
   } 
   return max; 
}