Today I had occasion to use in a work project the PriorityQueue<T> and Heap code that I had written and blogged about recently. In doing so, I discovered a couple of bugs and fixed them and added tests to cover the issue that was uncovered.

Here’s what changed in the PriorityQueue<T>. You can follow the link above to see the change to Heap.

// before
public void Enqueue(T item, T minItem, T maxItem)
{
   if (_order == PriorityOrder.Max)
      Heap.MaxInsert(_data, item, maxItem, _heapSize++);
   else
      Heap.MinInsert(_data, item, minItem, _heapSize++);
}

// after
public void Enqueue(T item, T minItem, T maxItem)
{
   if (_order == PriorityOrder.Max)
      Heap.MaxInsert(_data, item, minItem, _heapSize++);
   else
      Heap.MinInsert(_data, item, maxItem, _heapSize++);
}

And here is the full code for PriorityQueue<T>:

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace AlgoLib.Structures
{
   public enum PriorityOrder
   {
      Min,
      Max
   }

   public class PriorityQueue<T> : IEnumerable<T>, 
      ICollection, IEnumerable where T : IComparable
   {
      private readonly PriorityOrder _order;
      private readonly IList<T> _data;
      private int _heapSize = 0;

      public PriorityQueue(PriorityOrder order)
      {
         _data = new List<T>();
         _order = order;
      }

      public PriorityQueue(IEnumerable<T> data, PriorityOrder order)
      {
         _data = data as IList<T>;
         if (_data == null) _data = new List<T>(data);
         _order = order;
         _heapSize = _data.Count;
         if (_order == PriorityOrder.Max)
            Heap.BuildMaxHeap(_data);
         else
            Heap.BuildMinHeap(_data);
      }

      public PriorityQueue(int initialCapacity, PriorityOrder order)
      {
         _data = new List<T>(initialCapacity);
         _order = order;
      }

      public void Clear()
      {
         _data.Clear();
      }

      public bool Contains(T item)
      {
         if (_order == PriorityOrder.Max)
            return Heap.MaxContains(_data, item, 0, _heapSize);
         else
            return Heap.MinContains(_data, item, 0, _heapSize);
      }

      public T Dequeue()
      {
         if (_heapSize == 0) throw new InvalidOperationException();
         if (_order == PriorityOrder.Max)
            return Heap.ExtractMax(_data, _heapSize--);
         else
            return Heap.ExtractMin(_data, _heapSize--);
      }

      public void Enqueue(T item, T minItem, T maxItem)
      {
         if (_order == PriorityOrder.Max)
            Heap.MaxInsert(_data, item, minItem, _heapSize++);
         else
            Heap.MinInsert(_data, item, maxItem, _heapSize++);
      }

      public T Peek()
      {
         return _data[0];
      }

      public void TrimExcess()
      {
         // trim remove items in _data beyond _heapSize
         while (_heapSize < _data.Count)
         {
            _data.RemoveAt(_data.Count - 1);
         }
      }

      public T[] ToArray()
      {
         return _data.ToArray();
      }

      public IEnumerator<T> GetEnumerator()
      {
         return _data.GetEnumerator();
      }

      IEnumerator IEnumerable.GetEnumerator()
      {
         return _data.GetEnumerator();
      }

      public void CopyTo(Array array, int index)
      {
         _data.CopyTo((T[])array, index);
      }

      public int Count
      {
         get { return _heapSize; }
      }

      public int Size
      {
         get { return _data.Count; }
      }

      public bool IsSynchronized
      {
         get { return false; }
      }

      public object SyncRoot
      {
         get { return _data; }
      }
   }
}

If you like it, let me know.