Question

package algs24;

import stdlib.StdIn;

import stdlib.StdOut;

/**

* The <tt>PtrHeap</tt> class is the priorityQ class from Question 2.4.24.

* It represents a priority queue of generic keys.

*  

* It supports the usual <em>insert</em> and <em>delete-the-maximum</em>

* operations, along with methods for peeking at the maximum key,

* testing if the priority queue is empty, and iterating through

* the keys.

* For additional documentation, see <a href="http://algs4.cs.princeton.edu/24pq">Section 2.4</a> of

* <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.

*/

public class PtrHeap<K extends Comparable<? super K>> {

@SuppressWarnings("unchecked")

/** Create an empty priority queue */

public PtrHeap() {

}

/** Is the priority queue empty? */

public boolean isEmpty() { return true; }

/** Is the priority queue full? */

public boolean isFull() { return true; }

/** Return the number of items on the priority queue. */

public int size() { return 0; }

/**

* Return the largest key on the priority queue.

* Throw an exception if the priority queue is empty.

*/

public K max() {return null;

}

/** Add a new key to the priority queue. */

public void insert(K x) { return;

}

/**

* Delete and return the largest key on the priority queue.

* Throw an exception if the priority queue is empty.

*/

public K delMax() {return null;

}

private void showHeap() {

// a method to print out the heap

// useful for debugging

}

public static void main(String[] args) {

PtrHeap<String> pq = new PtrHeap<>();

StdIn.fromString("10 20 30 40 50 - - - 05 25 35 - - - 70 80 05 - - - - ");

while (!StdIn.isEmpty()) {

StdOut.print ("pq: "); pq.showHeap();

String item = StdIn.readString();

if (item.equals("-")) StdOut.println("max: " + pq.delMax());

else pq.insert(item);

}

StdOut.println("(" + pq.size() + " left on pq)");

}

}

Answer 1

Import StdIn and StdOut and then run the program.

import stdlib.StdIn;
import stdlib.StdOut;

public class PtrHeap<K extends Comparable<? super K>> {

    private K[] pq;                    // store items at indices 1 to N
    private int N;                       // number of items on priority queue
    private int MAXN;

    @SuppressWarnings("unchecked")
    /** Create an empty priority queue */
    public PtrHeap(int initCapacity) {

        MAXN = initCapacity;
        pq = (K[]) new Comparable[initCapacity + 1];
        N = 0;
    }

    /** Is the priority queue empty? */
    public boolean isEmpty() { return N == 0; }

    /** Is the priority queue full? */
    //public boolean isFull() { return N == MAXN; }

    /** Return the number of items on the priority queue. */
    public int size() { return N; }

    /**
     * Return the largest key on the priority queue.
     * Throw an exception if the priority queue is empty.
     */
    public K max() {

        if (isEmpty()) throw new Error("Priority queue underflow");
        return pq[1];

    }

    /** Add a new key to the priority queue. */
    public void insert(K x) {
        //if (isFull()) throw new Error("Priority queue overflow");
        pq[++N] = x;

    }

    /**
     * Delete and return the largest key on the priority queue.
     * Throw an exception if the priority queue is empty.
     */
    public K delMax() {
        if (N == 0) throw new Error("Priority queue underflow");
        K max = pq[1];
        pq[N+1] = null;
        return max;
    }

    private void showHeap() {
        // a method to print out the heap
        for (int i = 1; i <= N; i++)
            StdOut.print (pq[i] + " ");
        StdOut.println ();
    }

    public static void main(String[] args) {
        PtrHeap<String> pq = new PtrHeap<>(100);
        StdIn.fromString("10 20 30 40 50 - - - 05 25 35 - - - 70 80 05 - - - - ");
        while (!StdIn.isEmpty()) {
            StdOut.print ("pq: "); pq.showHeap();
            String item = StdIn.readString();
            if (item.equals("-")) StdOut.println("max: " + pq.delMax());
            else pq.insert(item);
        }
        StdOut.println("(" + pq.size() + " left on pq)");

    }

}