code: package zemberek.core.dynamic;
  
  import java.util.Iterator;
  
  /**
   * This is a special set like data structure that can be used in beam-search like algorithms. It
   * holds objects with a {@link Scorable} interface.
   *
   * When an object is added to the ActiveList, it checks if an equivalent object exists. If not,
   * object is placed in the data structure using linear probing. If an equivalent object exists
   * object with lower score is replaced with the the other one.
   */
  public class ActiveList<T extends Scorable> implements Iterable<T> {
  
    static float DEFAULT_LOAD_FACTOR = 0.55f;
  
    static int DEFAULT_INITIAL_CAPACITY = 8;
  
    private T[] items;
  
    private int modulo;
    private int size;
    private int expandLimit;
  
    public ActiveList() {
      this(DEFAULT_INITIAL_CAPACITY);
    }
  
    public ActiveList(int size) {
      if (size < 1) {
        throw new IllegalArgumentException("Size must be a positive value. But it is " + size);
      }
      int k = 1;
      while (k < size) {
        k <<= 1;
      }
      items = (T[]) new Scorable[k];
      expandLimit = (int) (k * DEFAULT_LOAD_FACTOR);
      modulo = k - 1;
    }
  
    private int rehash(int key) {
      final int h = key * 0x9E3779B9;
      return (h ^ (h >> 16)) & 0x7fff_ffff;
    }
  
    /**
     * Finds either an empty slot location in Hypotheses array or the location of an equivalent item.
     * If an empty slot is found, it returns -(slot index)-1, if an equivalent item is found, returns
     * equal item's slot index.
     */
    private int locate(T t) {
      int slot = rehash(t.hashCode()) & modulo;
      while (true) {
        final Scorable h = items[slot];
        if (h == null) {
          return (-slot - 1);
        }
        if (h.equals(t)) {
          return slot;
        }
        slot = (slot + 1) & modulo;
      }
    }
  
    /**
     * Adds a new scorable to the list.
     **/
    public void add(T t) {
  
      int slot = locate(t);
  
      // if not exist, add.
      if (slot < 0) {
        slot = -slot - 1;
        items[slot] = t;
        size++;
      } else {
        // If exist, check score and if score is better, replace it.
        if (items[slot].getScore() < t.getScore()) {
          items[slot] = t;
        }
      }
      if (size == expandLimit) {
        expand();
      }
    }
  
    private void expand() {
      ActiveList<T> expandedList = new ActiveList<>(items.length * 2);
      // put items to new list.
      for (int i = 0; i < items.length; i++) {
        T t = items[i];
        if (t == null) {
          continue;
        }
        int slot = rehash(t.hashCode()) & modulo;
        while (true) {
          final T h = expandedList.items[slot];
          if (h == null) {
            expandedList.items[slot] = t;
            break;
          }
          slot = (slot + 1) & modulo;
        }
      }
      this.modulo = expandedList.modulo;
      this.expandLimit = expandedList.expandLimit;
      this.items = expandedList.items;
    }
  
    public T getBest() {
      T best = null;
      for (T t : items) {
        if (t == null) {
          continue;
        }
        if (best == null || t.getScore() > best.getScore()) {
          best = t;
        }
      }
      return best;
    }
  
    @Override
    public Iterator<T> iterator() {
      return new TIterator();
    }
  
    class TIterator implements Iterator<T> {
  
      int pointer = 0;
      int count = 0;
      T current;
  
      @Override
      public boolean hasNext() {
        if (count == size) {
          return false;
        }
        while (items[pointer] == null) {
          pointer++;
        }
        current = items[pointer];
        count++;
        pointer++;
        return true;
      }
  
      @Override
      public T next() {
        return current;
      }
    }
  }
  