Examples of net.sf.jsi.PriorityQueue

net.sf.jsi.PriorityQueue

Priority Queue that stores values as ints and priorities as floats. Uses a Heap to sort the priorities; the values are sorted "in step" with the priorities.

A Heap is simply an array that is kept semi sorted; in particular if the elements of the array are arranged in a tree structure; ie

 00 /     \ 01          02 /  \        /  \ 03    04    05    06 /\    /\    /\    /\ 07 08 09 10 11 12 13 14

then each parent is kept sorted with respect to it's immediate children. E.g. 00 < 01, 00 < 02, 02 < 05, 02 < 06

This means that the array appears to be sorted, as long as we only ever look at element 0.

Inserting new elements is much faster than if the entire array was kept sorted; a new element is appended to the array, and then recursively swapped with each parent to maintain the "parent is sorted w.r.t it's children" property.

To return the "next" value it is necessary to remove the root element. The last element in the array is placed in the root of the tree, and is recursively swapped with one of it's children until the "parent is sorted w.r.t it's children" property is restored.

Random access is slow (eg for deleting a particular value), and is not implemented here - if this functionality is required, then a heap probably isn't the right data structure.

    //
    // Uses a priority queue as the underlying data structure.
    //
    // Note that more than N items will be returned if items N and N+x have the
    // same priority.
    PriorityQueue distanceQueue = new PriorityQueue(PriorityQueue.SORT_ORDER_DESCENDING);
    createNearestNDistanceQueue(p, count, distanceQueue, furthestDistance);


    while (distanceQueue.size() > 0) {
      v.execute(distanceQueue.getValue());
      distanceQueue.pop();
    }
  }


  /**
   * @see net.sf.jsi.SpatialIndex#nearestN(Point, TIntProcedure, int, float)
   */
  public void nearestN(Point p, TIntProcedure v, int count, float furthestDistance) {
    PriorityQueue distanceQueue = new PriorityQueue(PriorityQueue.SORT_ORDER_DESCENDING);
    createNearestNDistanceQueue(p, count, distanceQueue, furthestDistance);
    distanceQueue.setSortOrder(PriorityQueue.SORT_ORDER_ASCENDING);


    while (distanceQueue.size() > 0) {
      v.execute(distanceQueue.getValue());
      distanceQueue.pop();
    }
  }

Related Classes of net.sf.jsi.PriorityQueue

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