Download Lecture 1 - Computer Science

SoloSnap: A Simple Card Game
Lecture 1: Case Study: SoloSnap
CS2504/CS4092– Algorithms and Linear Data Structures
Rules of SoloSnap
Shuffle deck
Deal cards one by one until either
Dr Kieran T. Herley
snap 1 occurs (player wins), or
run out of cards (player loses)
Department of Computer Science
University College Cork
Challenge Develop Java application to simulate SoloSnap
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Two consecutive cards with same value e.g. two kings, two sevens, etc.
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Class Card
Towards a Java Implementation
Class Card
Requirements
Each card to encode suit, value
Operations
Our application will employ three Java classes
probe suit
probe value
print card
Card abstraction of playing card
DeckOfCards abstraction of deck container
SoloSnap implementation of game using above classes
Ideas
Rep. suit, value by ints
Getters for these
toString method useful
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Class Card
Class Card
Class Card.java–skeleton 1
Class Card.java–skeleton 2
We need some getters and setters for suit and value, so . . .
public class Card
{ public Card(int s , int v)
{ value = v; suit = s;
}
public int getSuit ()
{ return suit ;
}
public int getValue()
{ return value ;
}
. . .
private int suit ;
private int value ;
public class Card
{ public Card(int s , int v)
{ value = v; suit = s;
}
. . .
. . .
private int suit ;
private int value ;
}
}
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Class Card
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Class Card
Using Class Card
Using Class Constants
Add named class constants to Card.java
Card.java: a “blueprint” for card objects
/∗ Suit encodings ∗/
public static final int
public static final int
public static final int
public static final int
// Create 2 of Diamonds
Card c1 = new Card(2, 2);
// Create ace of hearts
Card c2 = new Card(4, 14);
/∗ Value encodings ∗/
public static final int
. . .
public static final int
public static final int
public static final int
public static final int
public static final int
// Create four of clubs
Card c3 = new Card(3, 4);
Awkward: Need to remember “encoding” of suits etc.
HEARTS = 4;
CLUBS = 3;
DIAMONDS = 2;
SPADES = 1;
TWO = 2;
TEN = 10;
JACK = 11;
QUEEN = 12;
KING = 13;
ACE = 14;
2
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Note: Using an enum would be far better for this.
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Class Card
Class Card
Using Class Constants cont’d
A Useful Method
Would be nice to be able to display cards as text e.g. “Ace of Hearts”
rather than cryptic “4 14”.
// Create 2 of Diamonds
Card c1 = new Card(Card.DIAMONDS, Card.TWO);
private String suitAsString ()
{ switch ( getSuit ())
{ case Card.HEARTS:
return ”Hearts”;
case Card.CLUBS:
return ”Clubs”;
case Card.DIAMONDS: return ”Diamonds”;
case Card.SPADES:
return ”Spades”;
}
return ””;
}
// Create ace of hearts
Card c2 = new Card(Card.HEARTS, Card.ACE);
// Create four of clubs
Card c3 = new Card(Card.CLUBS, Card.FOUR);
NB Syntax Classname-dot-Constantname; also far-more readable
public String toString ()
{ return valueAsString()+” of ”+suitAsString();
}
Note: Java also provides a mechanism for enumerated types that
provide a clearer soloution to this problem but we ignore this
possibility for simplicity. See Card2.java for details.
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NB “helper” method private
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Class Card
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Class DeckOfCards
Class Card
Class DeckOfCards
public class Card
{ public Card(int s , int v)
{ value = v; suit = s;
}
public int getSuit ()
{ return suit ;
}
public int getValue()
{ return value ;
}
Requirements
/∗ Suit encodings ∗/
public static final int HEARTS = 4;
. . .
public void print ()
{ System.out. println (
valueAsString()+” of ”+
suitAsString ());
}
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/∗ Value encodings ∗/
public static final int TWO = 2;
public static final int THREE = 3;
public static final int FOUR = 4;
. . .
Represent collection of cards i.e. is a container
Operations
(add card)
shuffle cards
remove card
probe emptiness
Ideas
Use array to hold cards
Use random swaps for shuffling
private int suit ;
private int value ;
}
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Class DeckOfCards
Class DeckOfCards
Representation for DeckOfCards–Left-Justified Array
Adding a Card
array of (≤ 52) (references to) Card objects
left-justified array
numCards cards in deck occupy slots 0 to numCards − 1 inclusive, i.e.
compacted in left side of array, no “gaps”
Place new item in leftmost unoccupied slot (index numCards)
Increment numCards
slots n upwards are “empty”
additions/removals preserve this property
need array plus number-of-cards variable (here numCards)
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Class DeckOfCards
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Class DeckOfCards
Removing a Card
Skeleton of DeckOfCards.java – 1
public class
{
. . .
}
Extract item from rightmost occupied slot (index numCards − 1)
DeckOfCards
Decrement numCards
Return item
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Class DeckOfCards
Class DeckOfCards
Skeleton of DeckOfCards.java – 2
public class
{
. . .
Skeleton of DeckOfCards.java – 3
public class DeckOfCards
{
public DeckOfCards()
{ theCards = new Card[FULLDECKSIZE];
numCards = 0;
DeckOfCards
addAllCards ();
private static final int FULLDECKSIZE = 52;
private Card[] theCards;
private int numCards;
} .
.
}
private void addAllCards()
{ . . .}
NB Declaration of theCards does not create an array; this variable is
initially null.
. . .
private static final int FULLDECKSIZE = 52;
private Card[] theCards;
private int numCards;
}
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Class DeckOfCards
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Class DeckOfCards
Initialization–addAllCards cont’d
Initialization–addAllCards cont’d
private void addAllCards()
{ for (int s = Card.FIRSTSUIT; s <= Card.LASTSUIT; s++)
{ for (int v = Card.FIRSTVALUE; v <= Card.LASTVALUE; v++)
{ /∗ add card for suit s and value v
}
}
}
Card.FIRSTSUIT etc. better than “embedded constants” 1 etc.
Iterates through all 52 suit-value combinations, creates the
corresponding cards, and places each in a distinct slot of the array
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private void addAllCards()
{ for (int s = Card.FIRSTSUIT; s <= Card.LASTSUIT; s++)
{ for (int v = Card.FIRSTVALUE; v <= Card.LASTVALUE; v++)
{ theCards[numCards] = new Card(s, v);
numCards++;
}
}
}
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Again, this would be cleaner with enums.
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Class DeckOfCards
Class DeckOfCards
Simple Operations–removeCard
Simple Operations–isEmpty
Representation
Representation
removeCard public Card removeCard()
{ numCards−−;
return theCards[numCards];
}
isEmpty public boolean isEmpty()
{ return (numCards == 0);
}
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Class DeckOfCards
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Class DeckOfCards
Shuffling
Shuffling cont’d
Idea
import java. util .Random;
. . .
Random randomNumGen = new Random();
. . .
int rand = randomNumGen.nextInt(N);
Repeat following “many” times
Pick two array positions at random
Swap cards at those two positions
Random Numbers Java class java.util.Random provides source of
random ints etc.
Quantifying “Many” Statistical calculation; we choose ten times
number of cards
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Details See code
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SoloSnap
SoloSnap
The Story So Far
Warmup Exercise
Exercise Shuffle deck, remove cards one by one and print them
A lot done . . .
Code Snippet
Card.java
playing card abstraction
Operations: getSuit, getValue, print
DeckOfCards.java
DeckOfCards deck = new DeckOfCards();
deck. shuffle ();
while (! deck.isEmpty())
{ currentCard = deck.removeCard();
System.out. println (currentCard . toString ());
}
deck of cards abstraction
Operations: shuffle, removeCard, isEmpty
More to do Implement SoloSnap using above classes
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SoloSnap
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SoloSnap
SoloSnap 1
SoloSnap
public class SoloSnap
{ public static void main(String [] args)
{ DeckOfCards deck = new DeckOfCards();
deck. shuffle ();
public class SoloSnap
{ public static void main(String [] args)
{ DeckOfCards deck = new DeckOfCards(); // create and shuffle deck
deck. shuffle ();
Card currentCard = null;
Card prevCard = null;
boolean snapFound = false;
. . .
}
// Current and previous card
// True if snap found
. . .
}
if (snapFound){...} else {...}
// Print outcome
}
}
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SoloSnap
SoloSnap
SoloSnap
SoloSnap
public class SoloSnap
{ public static void main(String [] args)
{ DeckOfCards deck = new DeckOfCards(); deck.shuffle();
public class SoloSnap
{ public static void main(String [] args)
{ DeckOfCards deck = new DeckOfCards(); deck.shuffle();
Card currentCard = null;
Card prevCard = null;
boolean snapFound = false;
Card currentCard = null;
Card prevCard = null;
boolean snapFound = false;
while (! deck.isEmpty() && ! snapFound)
{ . . .
currentCard = deck.removeCard();
System.out. println (currentCard . toString ());
. . .
}
while (! deck.isEmpty() && ! snapFound)
{ prevCard = currentCard;
// Remember prev. card
currentCard = deck.removeCard();
System.out. println (currentCard . toString ());
if (prevCard != null)
// Compare curent and prev. cards
{ snapFound = (currentCard.getValue() == prevCard.getValue());
}
if (snapFound){...} else {...}
}
}
}
if (snapFound){...} else {...}
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SoloSnap
Points to Note
Design: multiple classes, each encapsulating one coherent concept
DeckOfCards as “container”
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}
}
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