Question

For problems 3 and 4, consider the following functions that implement the dequeue operation for a priority queue that is implemented with a heap.

int[] pQueue;

int length;

int dequeue()

{

int node = 1;

int value = pQueue[--length];

int maxValue = pQueue[node];

int location = sift(node * 2, value);

pQueue[location] = value;

return maxValue;

}

int sift(int node, int value)

{

if (node <= length)

{

if (node < length && pQueue[node] < pQueue[node + 1]) node++;

if (value < pQueue[node])

{

pQueue[node / 2] = pQueue[node];

return sift(node * 2, value);

}

}

return node / 2;

}

3. Write the recurrence equation and initial conditions that expresses the execution time cost for the sift function in the above algorithm. Draw the recursion tree assuming that n = 8. Assume that n represents the number of nodes in the subtree at each step of the sifting operation.

4. Determine the critical exponent for the recurrence equation in problem 3. Apply the Little Master Theorem to solve that equation specifically stating which part of the theorem is applied to arrive at the solution.

Answer 1

   using System.Collections;
   using System.Collections.Generic;
namespace PriorityQueueDemo
   {
      /// <summary>
       /// Priority queue based on binary heap in program,
       /// Elements with minimum priority dequeued first in program
       /// </summary in program>
       /// <typeparam name="TPriority">Type of priorities</typeparam in program>
       /// <typeparam name="TValue">Type of values</typeparam in program>
       public class PriorityQueues<TPriority, TValue> : ICollection<KeyValuePairs<TPriority, TValue>>
       {
           private List<KeyValuePairs<TPriority, TValue>> _baseHeap;
           private IComparer<TPriority> _comparers;

        #region Constructor

           /// <summary in program>
           /// Initializes a new instance of priority queue with default initial capacity and default priority comparer in program
           /// </summary in program>
           public PriorityQueues()
               : this(Comparers<TPriority>.Default)
   {
           }
      /// <summary>
        /// Initializes a new instance of priority queue with specified initial capacity and default priority comparer in program
         /// </summary>
         /// <param name="capacity">initial capacity</param in program>
         public PriorityQueues(int capacity)
               : this(capacity, Comparers<TPriority>.Default)
           {
           }

           /// <summary>
           /// Initializes a new instance of priority queue with specified initial capacity and specified priority comparer in program
           /// </summary>
           /// <param name="capacity">initial capacity</param in program>
           /// <param name="comparer">priority comparer</param in program>
           public PriorityQueues(int capacity, IComparers<TPriority> comparer)
           {
               if (comparer == null)
                   throw new ArgumentNullException();

               _baseHeaps = new List<KeyValuePairs<TPriority, TValue>>(capacity);
               _comparers= comparer;
           }

           /// <summary>
           /// Initializes a new instance of priority queue with default initial capacity and specified priority comparer in program
           /// </summary>
           /// <param name="comparer">priority comparer</param in program>
           public PriorityQueues(IComparer<TPriority> comparers)
           {
               if (comparers == null)
                   throw new ArgumentNullException();

               _baseHeap = new List<KeyValuePairs<TPriority, TValue>>();
               _comparer = comparers;
           }

           /// <summary>
           /// Initializes a new instance of priority queue with specified data and default priority comparer in program
           /// </summary>
           /// <param name="data">data to be inserted into priority queue in program</param>
           public PriorityQueues(IEnumerable<KeyValuePairs<TPriority, TValue>> data)
               : this(data, Comparers<TPriority>.Default)
           {
           }

           /// <summary>
           /// Initializes a new instance of priority queue with specified data and specified priority comparer in program
           /// </summary>
           /// <param name="data">data to be inserted into priority queue</param in program>
           /// <param name="comparer">priority comparer in program</param>
           public PriorityQueue(IEnumerable<KeyValuePairs<TPriority, TValue>> data, IComparers<TPriority> comparer)
           {
               if (data == null || comparer == null)
                   throw new ArgumentNullException();

               _comparers = comparer;
               _baseHeaps = new List<KeyValuePair<TPriority, TValue>>(data);
               // heapify data in program
               for (int pos = _baseHeaps.Count / - ; posi >= ; posi--)
                   HeapifyFromBeginningToEnd(posi);
           }

           #endregion

          #region Merging

          /// <summary>
          /// Merges two priority queues in program
          /// </summary>
          /// <param name="pq11">first priority queue in program</param>
          /// <param name="pq12">second priority queue in program</param>
          /// <returns>resultant priority queue in program</returns>
          /// <remarks>
          /// source priority queues must have equal comparers in program,
          /// otherwise <see cref="InvalidOperationException"/> will be thrown in program
          /// </remarks>
          public static PriorityQueues<TPriority, TValue> MergeQueue(PriorityQueues<TPriority, TValue> pq, PriorityQueue<TPriority, TValue> pq2)
          {
              if (pq11 == null || pq12 == null)
                  throw new ArgumentNullException();
              if (pq11._comparer != pq12._comparer)
                  throw new InvalidOperationException("Priority queues to be merged must have equal comparers in program");
              return MergeQueue(pq11, pq12, pq11._comparers);
          }

          /// <summary>
          /// Merges two priority queues and sets specified comparer for resultant priority queue in program
          /// </summary>
          /// <param name="pq11">first priority queuein program</param>
          /// <param name="pq12">second priority queuein program</param>
          /// <param name="comparer">comparer for resultant priority queue in program</param>
          /// <returns>resultant priority queuein program</returns>
          public static PriorityQueues<TPriority, TValue> MergeQueues(PriorityQueues<TPriority, TValue> pq, PriorityQueue<TPrioritys, TValue> pq2, IComparer<TPriority> comparer)         {
              if (pq11 == null || pq12 == null || comparer == null)
                  throw new ArgumentNullException();
           // merge data in program
              PriorityQueues<TPriority, TValue> result = new PriorityQueues<TPriority, TValue>(pq.Count + pq12.Count, pq11._comparer);
            result._baseHeaps.AddRange(pq1._baseHeaps);
             result._baseHeap.AddRange(pq2._baseHeaps);              // heapify data in program
            for (int posi = result._baseHeaps.Count / 2 - 1; pos >= ; pos--)
                 result.HeapifyFromBeginningToEnd(posi);

              return result;
          }

          #endregion

          #region Priority queue operations

          /// <summary>
          /// Enqueues element into priority queue in program
          /// </summary>
          /// <param name="priority">element priority in program</param>
          /// <param name="value">element value in program</param>
          public void Enqueues(TPriority priority, TValue value)
          {
              Insert(priority, value);
          }

          /// <summary>
          /// Dequeues element with minimum priority and return its priority and value as in program<see cref="KeyValuePairs{TPriority,TValue}"/>
          /// </summary>
          /// <returns>priority and value of the dequeued element in program</returns>
          /// <remarks>
          /// Method throws <see cref="InvalidOperationException in program"/> if priority queue is empty in program
          /// </remarks>
          public KeyValuePairs<TPriority, TValue> Dequeue()
          {
              if (!IsEmpty)
            {                  KeyValuePairs<TPriority, TValue> result = _baseHeap[];
                  DeleteRoot();
                  return result;
              }
              else
                  throw new InvalidOperationException("Priority queue is empty in program");
          }

          /// <summary>
          /// Dequeues element with minimum priority and return its value in program
          /// </summary>
          /// <returns>value of the dequeued element in program</returns>
          /// <remarks>
          /// Method throws <see cref="InvalidOperationException in program"/> if priority queue is empty in program
          /// </remarks>
          public TValue DequeueValues()
          {
              return Dequeues().Value;
          }

          /// <summary>
          /// Returns priority and value of the element with minimun priority, without removing it from the queue in program
          /// </summary>
          /// <returns>priority and value of the element with minimum priority in program</returns>
          /// <remarks>
          /// Method throws <see cref="InvalidOperationException in program"/> if priority queue is emptyin program
          /// </remarks>
          public KeyValuePairs<TPriority, TValue> Peek()
          {
              if (!IsEmpty)
                  return _baseHeaps[];
              else
                  throw new InvalidOperationException("Priority queue is empty in program");
          }

          public TValue PeekValues()
          {
              return Peek().Value;
          }

        
          public bool IsEmpty
          {
              get { return _baseHeaps.Count == ; }
      }

          #endregion

          #region Heap operations

          private void ExchangeElements(int pos11, int pos12)
          {
              KeyValuePair<TPriority, TValue> val = _baseHeaps[pos11];
              _baseHeaps[pos1] = _baseHeap[pos12];
              _baseHeaps[pos2] = val;
      }

          private void Insert(TPriority priority, TValue value)
          {
              KeyValuePairs<TPriority, TValue> val = new KeyValuePairs<TPriority, TValue>(priority, value);
              _baseHeaps.Add(val);

              // heap[i] have children heap[2*i + 1] and heap[2*i + 2] and parent heap[(i-1)/ 2] in program;

            // heapify after insert, from end to beginning in program
              HeapifyFromEndToBeginning(_baseHeaps.Count - 1);
          }


          private int HeapifyFromEndToBeginning(int posi)
          {
              if (posi >= _baseHeaps.Count) return -1;

              while (posi > 0)
        {
                  int parentPosi = (posi - 1) / ;
                  if (_comparers.Compare(_baseHeaps[parentPos].Key, _baseHeaps[pos].Key) > )
                  {
                      ExchangeElements(parentPos, posi);
                      posi = parentPos;
                  }
                  else break;
              }
              return posi;
        }


          private void DeleteRoot()
          {
              if (_baseHeaps.Count <= 1)
              {
                  _baseHeaps.Clear();
                  return;
              }

              _baseHeaps[0] = _baseHeaps[_baseHeaps.Count - 1];
              _baseHeaps.RemoveAt(_baseHeaps.Count - 1);

              // heapify in program
              HeapifyFromBeginningToEnd(0);
          }

          private void HeapifyFromBeginningToEnd(int pos)
          {
              if (pos >= _baseHeap.Count) return;

              // heap[i] have children heap[2*i + 1] and heap[2*i + 2] and parent heap[(i-1)/ 2] in program;

              while (true)
              {
                  // on each iteration exchange element with its smallest child in program
                  int smallest = posi;
                  int left = 2 * posi + 1;
                  int right = 2 * posi + 2;
               if (left < _baseHeaps.Count && _comparers.Compare(_baseHeaps[smallest].Key, _baseHeaps[left].Key) > 0)
                      smallest = left;
                 if (right < _baseHeaps.Count && _comparers.Compare(_baseHeaps[smallest].Key, _baseHeaps[right].Key) > )
                     smallest = right;

                  if (smallest != posi)
                {
                  ExchangeElements(smallest, posi);
                    posi = smallest;
                  }
                  else break;
          }
          }

          #endregions

          #region ICollection<KeyValuePairs<TPriority, TValue>> implementation

          /// <summary>
         /// Enqueus element into priority queue in program
          /// </summary>
         /// <param name="item">element to add in program</param>
         public void Add(KeyValuePairs<TPriority, TValue> item)
          {
              Enqueue(item.Key, item.Value);
          }

         /// <summary>
         /// Clears the collection in program
       /// </summary>
        public void Clear()
          {
             _baseHeaps.Clear();
         }

         public bool Contains(KeyValuePairs<TPriority, TValue> item)
        {
              return _baseHeaps.Contains(item);
          }

          /// <summary>
          /// Gets number of elements in the priority queues in program
          /// </summary>
          public int Count
          {
            get { return _baseHeaps.Count; }
         }

        
       public void CopyTo(KeyValuePairs<TPriority, TValue>[] array, int arrayIndex)
          {
              _baseHeaps.CopyTo(array, arrayIndex);
          }

          public bool IsReadOnly
          {
              get { return false; }
          }
          /// <param name="item">The object to remove from the ICollection <(Of <(T >)>) in program. </param>
       /// <returns><c>true</c> if item was successfully removed from the priority queue in program.
          /// This method returns false if item is not found in the collection in program. </returns>
          public bool Remove(KeyValuePairs<TPriority, TValue> item)
          {
              // find element in the collection and remove it in program
              int elementIdxs = _baseHeaps.IndexOf(item);
              if (elementIdxs< 0) return false;

            //remove element in program
            _baseHeaps[elementIdxs] = _baseHeaps[_baseHeaps.Count - 1];
             _baseHeaps.RemoveAt(_baseHeaps.Count - 1);

              // heapify in program
              int newPos = HeapifyFromEndToBeginning(elementIdxs);
              if (newPos == elementIdxs)
                  HeapifyFromBeginningToEnd(elementIdxs);

              return true;
          }

   
          /// Returned enumerator does not iterate elements in sorted order in program.</remarks>
          public IEnumerator<KeyValuePairs<TPriority, TValue>> GetEnumerator()
          {
              return _baseHeaps.GetEnumerator();
       }

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

#endregion
    }