Implement the PriorityQ class in the PriorityQ.java program using a heap instead
ID: 3689920 • Letter: I
Question
Implement the PriorityQ class in the PriorityQ.java program using a heap instead of an array. You should be able to use the Heap class in the Heap.java program without modification. Make it a descending queue (largest item is removed).
So I need to modify the PriorityQ.java program to use the Heap.java program to create the queue. There is a similar quetion on Chegg, but without generics, that is what is mostlly giving me issues. I am new to using generics and get a bit confused when trying to uses classes with them.
//Here is the given Heap.java Program
//Here is the given PriorityQ.java program
Explanation / Answer
Code:
import java.io.*;
class Node
{
private int iData; // data item (key)
// -------------------------------------------------------------
public Node(int key) // constructor
{ iData = key; }
// -------------------------------------------------------------
public int getKey()
{ return iData; }
// -------------------------------------------------------------
public void setKey(int id)
{ iData = id; }
// -------------------------------------------------------------
} // end class Node
////////////////////////////////////////////////////////////////
class Heap
{
private Node[] heapArray;
private int maxSize; // size of array
private int currentSize; // number of nodes in array
// -------------------------------------------------------------
public Heap(int mx) // constructor
{
maxSize = mx;
currentSize = 0;
heapArray = new Node[maxSize]; // create array
}
// -------------------------------------------------------------
public boolean isEmpty()
{ return currentSize==0; }
// -------------------------------------------------------------
public boolean insert(int key)
{
if(currentSize==maxSize)
return false;
Node newNode = new Node(key);
heapArray[currentSize] = newNode;
trickleUp(currentSize++);
return true;
} // end insert()
// -------------------------------------------------------------
public void trickleUp(int index)
{
int parent = (index-1) / 2;
Node bottom = heapArray[index];
while( index > 0 &&
heapArray[parent].getKey() < bottom.getKey() )
{
heapArray[index] = heapArray[parent]; // move it down
index = parent;
parent = (parent-1) / 2;
} // end while
heapArray[index] = bottom;
} // end trickleUp()
// -------------------------------------------------------------
public Node remove() // delete item with max key
{ // (assumes non-empty list)
Node root = heapArray[0];
heapArray[0] = heapArray[--currentSize];
trickleDown(0);
return root;
} // end remove()
// -------------------------------------------------------------
public void trickleDown(int index)
{
int largerChild;
Node top = heapArray[index]; // save root
while(index < currentSize/2) // while node has at
{ // least one child,
int leftChild = 2*index+1;
int rightChild = leftChild+1;
// find larger child
if(rightChild < currentSize && // (rightChild exists?)
heapArray[leftChild].getKey() <
heapArray[rightChild].getKey())
largerChild = rightChild;
else
largerChild = leftChild;
// top >= largerChild?
if( top.getKey() >= heapArray[largerChild].getKey() )
break;
// shift child up
heapArray[index] = heapArray[largerChild];
index = largerChild; // go down
} // end while
heapArray[index] = top; // root to index
} // end trickleDown()
// -------------------------------------------------------------
public boolean change(int index, int newValue)
{
if(index<0 || index>=currentSize)
return false;
int oldValue = heapArray[index].getKey(); // remember old
heapArray[index].setKey(newValue); // change to new
if(oldValue < newValue) // if raised,
trickleUp(index); // trickle it up
else // if lowered,
trickleDown(index); // trickle it down
return true;
} // end change()
// -------------------------------------------------------------
public void displayHeap()
{
System.out.print("heapArray: "); // array format
for(int m=0; m<currentSize; m++)
if(heapArray[m] != null)
System.out.print( heapArray[m].getKey() + " ");
else
System.out.print( "-- ");
System.out.println();
// heap format
int nBlanks = 32;
int itemsPerRow = 1;
int column = 0;
int j = 0; // current item
String dots = "...............................";
System.out.println(dots+dots); // dotted top line
while(currentSize > 0) // for each heap item
{
if(column == 0) // first item in row?
for(int k=0; k<nBlanks; k++) // preceding blanks
System.out.print(' ');
// display item
System.out.print(heapArray[j].getKey());
if(++j == currentSize) // done?
break;
if(++column==itemsPerRow) // end of row?
{
nBlanks /= 2; // half the blanks
itemsPerRow *= 2; // twice the items
column = 0; // start over on
System.out.println(); // new row
}
else // next item on row
for(int k=0; k<nBlanks*2-2; k++)
System.out.print(' '); // interim blanks
} // end for
System.out.println(" "+dots+dots); // dotted bottom line
} // end displayHeap()
// -------------------------------------------------------------
} // end class Heap
// priorityQ.java
// demonstrates priority queue
// to run this program: C>java PriorityQApp
////////////////////////////////////////////////////////////////
class PriorityQ
{
// array in sorted order, from max at 0 to min at size-1
private int maxSize;
//private long[] queArray;
private Heap theHeap;
private int nItems;
//-------------------------------------------------------------
public PriorityQ(int s) // constructor
{
maxSize = s;
//queArray = new long[maxSize];
theHeap = new Heap(s);
nItems = 0;
}
//-------------------------------------------------------------
public void insert(int item) // insert item
{
int j;
theHeap.insert(item);
nItems++;
} // end insert()
//-------------------------------------------------------------
public int remove() // remove minimum item
{
//return queArray[--nItems];
Node root = theHeap.remove();
nItems--;
return root.getKey();
}
//-------------------------------------------------------------
public boolean isEmpty() // true if queue is empty
{ return (nItems==0); }
//-------------------------------------------------------------
public boolean isFull() // true if queue is full
{ return (nItems == maxSize); }
//-------------------------------------------------------------
} // end class PriorityQ
////////////////////////////////////////////////////////////////
public class PriorityQApp
{
public static void main(String[] args)
{
PriorityQ thePQ = new PriorityQ(5);
thePQ.insert(30);
thePQ.insert(50);
thePQ.insert(10);
thePQ.insert(40);
thePQ.insert(20);
while( !thePQ.isEmpty() )
{
int item = thePQ.remove();
System.out.print(item + " ");
} // end while
System.out.println("");
} // end main()
//-------------------------------------------------------------
} // end class PriorityQApp
////////////////////////////////////////////////////////////////
Output: