CC-7 : Implement Stacks using PriorityQueue.

Description:

Given Stack elements that each have a node integer data and integer priority. The node’s priority value will be used to order the stack node in the Stack. Create and test a priority ordered Stack using a PriorityQueue.

Test cases and expected outputs:

Input Parameters	Expected outputs
StackUsingPriorityQueue stack= new StackUsingPriorityQueue(); stack.addByPriority(99,33); stack.addByPriority(14, 10); stack.addByPriority(77, 44); stack.addByPriority(34, 55); stack.addByPriority(21, 66); stack.addByPriority(82, 33); stack.printStack();	Stack nodes: 21 Priority: 66 34 Priority: 55 77 Priority: 44 82 Priority: 33 99 Priority: 33 14 Priority: 10

Pseudocode:

The Stack will use a PriorityQueue for storing data elements in a priority sorted manner. PriorityQue accepts a comparator called StackPrioComparator to sort input elements by priority.

addByPriority() method:

Create a StackPriorityNode instance, and set the nodes data and priority to it.

Call PriorityQueue .add() with StackPriorityNode instance, this will ad nodeinpropersorted priority manner into PriorityQueue, using the StackPrioComparator.

remove() method: Return value returned by PriorityQueue.remove().

Code:

public class StackUsingPriorityQueue {	
	
private PriorityQueue<StackPriorityNode> pq=
new PriorityQueue< StackPriorityNode >(new StackPrioComparator());	

public StackPriorityNode get() {
	return pq.peek();
}

public boolean addByPriority(int data, int priority){
	StackPriorityNode node=new StackPriorityNode();
	node.setNodeData(data);
	node.setPriority(priority);
	pq.add(node);
	return true;
}

public StackPriorityNode remove() {
	return pq.poll();
}

public int getSize() {
	return pq.size();
}

public void traverse() {
	Iterator<StackPriorityNode> itr=pq.iterator();
	while (itr.hasNext()) {
  		System.out.println(((StackPriorityNode)itr.next()).getNodeData());
  		
  	}
}			

private class StackPrioComparator implements Comparator {	
	public int compare(Object stackNode1, Object stackNode2) {
		int frstNm= ((StackPriorityNode)stackNode1).getPriority();
		int scndNm= ((StackPriorityNode)stackNode2).getPriority();
		int retVal=0;
		if (frstNm < scndNm) {retVal =1;} else {
			if (frstNm == scndNm) {retVal = 0;} else {
				if (frstNm > scndNm) {retVal = -1;}
			}
		}		
	return retVal;
	}	
}  
}

Click here to download and run code and test cases !

Below fully running code can be copied and run on Eclipse or other Java IDEs. Refer the classname in code below. If the class name below is "A", save the code below to a file named A.java before running it. Be sure to try your own test cases to enhance your understanding ! You can also tweak the code to optimize or add enhancements and custom features.

import java.util.Comparator;
import java.util.Iterator;
import java.util.PriorityQueue;

public class StackUsingPriorityQueue {	
	
private PriorityQueue<StackPriorityNode> pq=
new PriorityQueue< StackPriorityNode >(new StackPrioComparator());	

public StackPriorityNode get() {
	return pq.peek();
}

public boolean addByPriority(int data, int priority){
	StackPriorityNode node=this.new StackPriorityNode();
	node.setNodeData(data);
	node.setPriority(priority);
	pq.add(node);
	return true;
}

public StackPriorityNode remove() {
	return pq.poll();
}

public int getSize() {
	return pq.size();
}

public void traverse() {
	Iterator<StackPriorityNode> itr=pq.iterator();
	while (itr.hasNext()) {
  		System.out.println(((StackPriorityNode)itr.next()).getNodeData());
  		
  	}
}			

public void printStack() throws Exception    {
    
	System.out.println();
	System.out.println("****************************************************");
	System.out.println("Stack nodes: ");
	while (pq.size() !=0) {
		StackPriorityNode node=(StackPriorityNode)pq.remove();
  		System.out.println(node.getNodeData()+ " Priority: "+node.getPriority());
	   	} 
	System.out.println();
	System.out.println("****************************************************");
	System.out.println();
	Thread.sleep(2000);
	return;
}    
    
private class StackPrioComparator implements Comparator {	
	public int compare(Object stackNode1, Object stackNode2) {
		int frstNm= ((StackPriorityNode)stackNode1).getPriority();
		int scndNm= ((StackPriorityNode)stackNode2).getPriority();
		int retVal=0;
		if (frstNm < scndNm) {retVal =1;} else {
			if (frstNm == scndNm) {retVal = 0;} else {
				if (frstNm > scndNm) {retVal = -1;}
			}
		}		
	return retVal;
	}	
}  
  	
public static void main(String[] args) {
	
	try {
	StackUsingPriorityQueue stack=new StackUsingPriorityQueue();
	System.out.print("Add to Stack");
	stack.addByPriority(99,33);
	System.out.print("Add to Stack");
	stack.addByPriority(14, 10);
	System.out.print("Add to Stack");
	stack.addByPriority(77, 44);
	System.out.print("Add to Stack");
	stack.addByPriority(34, 55);
	System.out.print("Add to Stack");
	stack.addByPriority(21, 66);
	System.out.print("Add to Stack");
	stack.addByPriority(82, 33);
	stack.printStack();	
	
	}catch (Exception exception) {
		System.out.print("Exception: "+ exception);
	}
	
}

class StackPriorityNode  {	
	private int nodeData=0;	
	private int priority;
	
	public int getNodeData() {
		return nodeData;
	}
	public void setNodeData(int nodeData) {
		this.nodeData = nodeData;		
	}
	public int getPriority() {
		return priority;
	}
	public void setPriority(int priority) {
		this.priority = priority;
	}	

}
	
}