Question

The goal of this exercise is to implement the shuffling algorithm from this chapter.
1. In the repository for this book, you should find the file named Deck.java. Check that you can compile it in your environment.
2. Implement the randomInt method. You can use the nextInt method provided by java.util.Random, which we saw in Section 7.6. Hint: To avoid creating a Random object every time randomInt is invoked, consider defining a class variable.
3. Write a swapCards method that takes two indexes and swaps the cards at the given locations.
4. Fill in the shuffle method using the algorithm in Section 13.2.
Deck Info
import java.util.Arrays;
import java.util.Random;

public class Deck {
    private Card[] cards;
    public Deck() {
        this.cards = new Card[52];
        int index = 0;
        for (int suit = 0; suit <= 3; suit++) {
            for (int rank = 1; rank <= 13; rank++) {
                this.cards[index] = new Card(rank, suit);
                index++;
            }
        }
    }
    public Deck(int n) {
        this.cards = new Card[n];
    }
    public Card[] getCards() {
        return this.cards;
    }
    public void print() {
        for (Card card : this.cards) {
            System.out.println(card);
        }
    }
    public String toString() {
        return Arrays.toString(this.cards);
    }
    public void shuffle() {
    }
    private static int randomInt(int low, int high) {
        return 0;
    }
    private void swapCards(int i, int j) {
    }
    public void selectionSort() {
    }
    private int indexLowest(int low, int high) {
        return 0;
    }
    public Deck subdeck(int low, int high) {
        Deck sub = new Deck(high - low + 1);
        for (int i = 0; i < sub.cards.length; i++) {
            sub.cards[i] = this.cards[low + i];
        }
        return sub;
    }
    private static Deck merge(Deck d1, Deck d2) {
        return null;
    }
    public Deck almostMergeSort() {
        return this;
    }
    public Deck mergeSort() {
        return this;
    }

    public void insertionSort() {
    }
}
7.6 randomInt Example
public static int[] randomArray(int size) {
   Random random = new Random();
   int[] a = new int[size];
   for (int i = 0; i < a.length; i++) {
       a[i] = random.nextInt(100);
       }
       return a;
}
Mentioned Shuffle Method
public void shuffle() {
   for each index i {
   // choose a random number between i and length - 1
   // swap the ith card and the randomly-chosen card
   }
}

Answer 1

Program Screenshot for Indentation Reference:

Program code to copy:

import java.util.Arrays;
import java.util.Random;

public class Deck {
    private Card[] cards;
    // Random Number Generator
    private static Random rand = new Random();

    public Deck() {
        this.cards = new Card[52];
        int index = 0;
        for (int suit = 0; suit <= 3; suit++) {
            for (int rank = 1; rank <= 13; rank++) {
                this.cards[index] = new Card(rank, suit);
                index++;
            }
        }

    }

    public Deck(int n) {
        this.cards = new Card[n];
    }

    public Card[] getCards() {
        return this.cards;
    }

    public void print() {
        for (Card card : this.cards) {
            System.out.println(card);
        }
    }

    public String toString() {
        return Arrays.toString(this.cards);
    }

    public void shuffle() {
        // shuffle the decks
        // loop over n-1 elements
        for (int i = 0; i < cards.length - 1; i++) {
            // get a random j such than i <= j < n and swap
            int j = randomInt(i, cards.length);
            // swap cards
            swapCards(i, j);
        }
    }

    private static int randomInt(int low, int high) {
        // return a random number p where low <= p < high
        // by adding low and getting a number between high - low
        return low + rand.nextInt(high - low);
    }

    private void swapCards(int i, int j) {

        // swap
        Card temp = cards[i];
        cards[i] = cards[j];
        cards[j] = temp;
    }

    public void selectionSort() {
    }

    private int indexLowest(int low, int high) {
        return 0;
    }

    public Deck subdeck(int low, int high) {
        Deck sub = new Deck(high - low + 1);
        for (int i = 0; i < sub.cards.length; i++) {
            sub.cards[i] = this.cards[low + i];
        }
        return sub;
    }

    private static Deck merge(Deck d1, Deck d2) {
        return null;
    }

    public Deck almostMergeSort() {
        return this;
    }

    public Deck mergeSort() {
        return this;
    }

    public void insertionSort() {
    }
}