13.9. Shuffling and dealing¶

In Section 13.6, I wrote pseudocode for a shuffling algorithm. Assuming that we have a function called shuffleDeck that takes a deck as an argument and shuffles it, we can create and shuffle a deck:

Deck deck;               // create a standard 52-card deck
deck.shuffleDeck ();     // shuffle it

Then, to deal out several hands, we can use subdeck:

Deck hand1 = deck.subdeck (0, 4);
Deck hand2 = deck.subdeck (5, 9);
Deck pack = deck.subdeck (10, 51);

This code puts the first 5 cards in one hand, the next 5 cards in the other, and the rest into the pack.

When you thought about dealing, did you think we should give out one card at a time to each player in the round-robin style that is common in real card games? I thought about it, but then realized that it is unnecessary for a computer program. The round-robin convention is intended to mitigate imperfect shuffling and make it more difficult for the dealer to cheat. Neither of these is an issue for a computer.

This example is a useful reminder of one of the dangers of engineering metaphors: sometimes we impose restrictions on computers that are unnecessary, or expect capabilities that are lacking, because we unthinkingly extend a metaphor past its breaking point. Beware of misleading analogies.

The active code below deals a deck of cards among three players for a game of Go Fish. Feel free to experiment with the code and deal decks for other games like War, Poker, and Egyptian Ratscrew.

#include <iostream>
#include <string>
#include <vector>
#include <cstdlib>
using namespace std;

enum Suit { CLUBS, DIAMONDS, HEARTS, SPADES };

enum Rank { ACE=1, TWO, THREE, FOUR, FIVE, SIX, SEVEN, EIGHT, NINE,
TEN, JACK, QUEEN, KING };

int randomInt (int low, int high);

struct Card {
    Rank rank;
    Suit suit;
    Card ();
    Card (Suit s, Rank r);
    void print () const;
    bool isGreater (const Card& c2) const;
    bool equals (const Card& c2) const;
};

struct Deck {
    vector<Card> cards;
    Deck ();
    Deck (int n);
    void print () const;
    void swapCards (int index1, int index2);
    int findLowestCard (int index);
    void shuffleDeck ();
    void sortDeck ();
    Deck subdeck (int low, int high) const;
};

int findBisect (Deck subdeck, Card card);

int main() {
    Deck deck;
    deck.shuffleDeck();
    Deck hand1 = deck.subdeck(0, 6);
    Deck hand2 = deck.subdeck(7, 13);
    Deck hand3 = deck.subdeck(14, 20);
    Deck pack = deck.subdeck(21, 51);
    cout << "Player 1's hand:" << endl;
    hand1.print();
    cout << endl;
    cout << "Player 2's hand:" << endl;
    hand2.print();
    cout << endl;
    cout << "Player 3's hand:" << endl;
    hand3.print();
}
====
Card::Card () {
    suit = SPADES;  rank = ACE;
}

Card::Card (Suit s, Rank r) {
    suit = s;  rank = r;
}

void Card::print () const {
    vector<string> suits (4);
    suits[0] = "Clubs";
    suits[1] = "Diamonds";
    suits[2] = "Hearts";
    suits[3] = "Spades";

vector<string> ranks (14);
    ranks[1] = "Ace";
    ranks[2] = "2";
    ranks[3] = "3";
    ranks[4] = "4";
    ranks[5] = "5";
    ranks[6] = "6";
    ranks[7] = "7";
    ranks[8] = "8";
    ranks[9] = "9";
    ranks[10] = "10";
    ranks[11] = "Jack";
    ranks[12] = "Queen";
    ranks[13] = "King";

cout << ranks[rank] << " of " << suits[suit] << endl;
}

bool Card::isGreater (const Card& c2) const {
    if (suit > c2.suit) return true;
    if (suit < c2.suit) return false;
    if (rank > c2.rank) return true;
    if (rank < c2.rank) return false;
    return false;
}

bool Card::equals (const Card& c2) const {
    return (rank == c2.rank && suit == c2.suit);
}

Deck::Deck () {
    vector<Card> temp (52);
    cards = temp;

int i = 0;
    for (Suit suit = CLUBS; suit <= SPADES; suit = Suit(suit+1)) {
        for (Rank rank = ACE; rank <= KING; rank = Rank(rank+1)) {
            cards[i].suit = suit;
            cards[i].rank = rank;
            i++;
        }
    }
}

Deck::Deck (int size) {
    vector<Card> temp (size);
    cards = temp;
}

void Deck::print () const {
    for (size_t i = 0; i < cards.size(); i++) {
        cards[i].print ();
    }
}

int randomInt (int low, int high) {
    srand (time(NULL));
    int x = random ();
    int y = x % (high - low + 1) + low;
    return y;
}

void Deck::swapCards (int index1, int index2) {
    Card temp = cards[index1];
    cards[index1] = cards[index2];
    cards[index2] = temp;
}

int Deck::findLowestCard (int index) {
    int min = index;
    for (size_t i = index; i < cards.size(); ++i) {
        if (cards[min].isGreater(cards[i])) {
            min = i;
        }
    }
    return min;
}

Deck Deck::subdeck (int low, int high) const {
    Deck sub (high-low+1);

for (size_t i = 0; i<sub.cards.size(); i++) {
        sub.cards[i] = cards[low+i];
    }
    return sub;
}

int findBisect (Deck subdeck, Card card) {
    if (subdeck.cards.size() == 1 && !subdeck.cards[0].equals(card)) return -1;
    int mid = subdeck.cards.size() / 2;
    if (subdeck.cards[mid].equals(card)) return mid;
    else if (subdeck.cards[mid].isGreater(card)) {
        return findBisect (subdeck.subdeck(0, mid - 1), card);
    }
    else {
        return findBisect (subdeck.subdeck(mid + 1, subdeck.cards.size()), card);
    }
}

void Deck::shuffleDeck () {
    for (size_t i = 0; i < cards.size(); i++) {
        int x = randomInt (i, cards.size() - 1);
        swapCards (i, x);
    }
}

void Deck::sortDeck () {
    for (size_t i = 0; i < cards.size(); i++) {
        int x = findLowestCard (i);
        swapCards (i, x);
    }
}

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13.9. Shuffling and dealing¶