// Maintains a list of ints. If you attempt to add() an int which has a 
// lower priority than any of the particles in the list, it will not be added;
// otherwise, it will be added, and one of the existing items dropped.
// Priorities must be positive.
class PriorityList {
  int count;
  int[] items;
  float[] priorities;
  
  PriorityList(int listLength) {
    count = listLength;
    items = new int[count];
    priorities = new float[count];
    for (int i = 0; i < count; i++) {
      items[i] = 0;
      priorities[i] = -1;
    }
  }
  
  void add(int item, float priority) {
    int index = 0;
    boolean addIt = false;
    for (int i = 0; i < count; i++) {
      // Find the item with the lowest priority in the list
      if (priorities[i] < 0.0) {
        index = i;
        addIt = true;
        break;
      }
      if (priority < priorities[i]) {
        index = i;
        addIt = true;
      }
    }
    if (addIt) {
      items[index] = item;
      priorities[index] = priority;
    }
  }
}