Playing Cards

For this question, we ask you to design a card game using the traditional 52-card deck. We divide this question into three parts, so you can complete them in order.

Part One

For the first part, you must design a Game class representing the game, and these following functions associated with the class.

  • add_card(suit, value): Creates a new card object with a suit from one of the following strings: Hearts, Spades, Clubs, Diamonds, and a value from one of the following strings: A, 2~10, J, Q, K. This card is represented by i, where i is an integer indicating how many cards have been created before.
  • card_string(card): Returns the string representation of the card represented by i. It follows the format <value> of <suit>. For example, a card created by add_card("Spades", "3") should have a string representation of 3 of Spades.
  • card_beats(card_a, card_b): Check if the card represented by card_a beats the one represented by card_b. A card beats another card if and only if it has a greater value. The value of the cards are ordered from A to K.

You may implement these however you like. However, preferably this should be easily expandable to accommodate new requirements.

Try it yourself

Solution

There are numerous approaches we can take to design this problem. The sample solution will provide an object-oriented approach, since it allows us to easily add new types of cards to accommodate new requirements.

Different languages have different tools, but the most basic concept in object oriented programming is inheritance, which is a class deriving from a superclass and inheriting its methods. In this situation, a playing card from the 52 is a card. The reason for this design is that we can easily add other types of cards if we want.

Below is an implementation:

1from enum import Enum, auto
2
3class Card:
4    @property
5    def card_value(self) -> int:
6        raise NotImplementedError()
7
8    def __lt__(self, other):
9        return self.card_value < other.card_value
10
11class Suit(Enum):
12    CLUBS = auto()
13    DIAMONDS = auto()
14    HEARTS = auto()
15    SPADES = auto()
16
17class PlayingCard(Card):
18    SUITS = {
19        "Clubs": Suit.CLUBS,
20        "Diamonds": Suit.DIAMONDS,
21        "Hearts": Suit.HEARTS,
22        "Spades": Suit.SPADES,
23    }
24    SUIT_NAMES = {e: n for n, e in SUITS.items()}
25    VALUES = {
26        "A": 1,
27        **{str(i): i for i in range(2, 11)},
28        "J": 11,
29        "Q": 12,
30        "K": 13,
31    }
32    VALUE_NAMES = {e: n for n, e in VALUES.items()}
33
34    def __init__(self, suit: str, value: str):
35        super().__init__()
36        self.__suit = self.SUITS[suit]
37        self.__value = self.VALUES[value]
38
39    @property
40    def card_value(self) -> int:
41        return self.__value
42
43    def __str__(self) -> str:
44        value = self.VALUE_NAMES[self.__value]
45        suit = self.SUIT_NAMES[self.__suit]
46        return f"{value} of {suit}"
47
48class Game:
49    def __init__(self):
50        self.__cards: list[Card] = []
51
52    def add_card(self, suit: str, value: str) -> None:
53        self.__cards.append(PlayingCard(suit, value))
54
55    def card_string(self, card: int) -> str:
56        return str(self.__cards[card])
57
58    def card_beats(self, card_a: Card, card_b: Card) -> bool:
59        return self.__cards[card_a] > self.__cards[card_b]
60
61if __name__ == '__main__':
62    game = Game()
63    suit, value = input().split()
64    game.add_card(suit, value)
65    print(game.card_string(0))
66    suit, value = input().split()
67    game.add_card(suit, value)
68    print(game.card_string(1))
69    print("true" if game.card_beats(0, 1) else "false")
70
1import java.util.ArrayList;
2import java.util.HashMap;
3import java.util.Map;
4import java.util.Scanner;
5import java.util.Map.Entry;
6import java.util.stream.Collectors;
7
8class Solution {
9    public static abstract class Card implements Comparable<Card> {
10        public abstract int getValue();
11
12        @Override
13        public int compareTo(Card o) {
14            return Integer.compare(getValue(), o.getValue());
15        }
16    }
17
18    public enum Suit {
19        SPADES, HEARTS, DIAMONDS, CLUBS
20    }
21
22    public static class PlayingCard extends Card {
23        private Suit suit;
24        private int value;
25
26        public static final Map<String, Suit> SUITS = Map.of(
27            "Spades", Suit.SPADES,
28            "Hearts", Suit.HEARTS,
29            "Diamonds", Suit.DIAMONDS,
30            "Clubs", Suit.CLUBS
31        );
32        // Inverts the above map to convert back to string.
33        public static final Map<Suit, String> SUIT_NAMES = SUITS.entrySet().stream().collect(Collectors.toMap(Map.Entry::getValue, Map.Entry::getKey));
34
35        // Map.of is limited to 10 entries, so we initialize a static map instead
36        public static final Map<String, Integer> VALUES = new HashMap<>();
37        static {
38            VALUES.put("A", 1);
39            for (int i = 2; i <= 10; i++) {
40                VALUES.put(String.valueOf(i), i);
41            }
42            VALUES.put("J", 11);
43            VALUES.put("Q", 12);
44            VALUES.put("K", 13);
45        }
46        // Inverts the above map to convert back to string.
47        public static final Map<Integer, String> VALUE_NAMES = VALUES.entrySet().stream().collect(Collectors.toMap(Map.Entry::getValue, Map.Entry::getKey));
48
49        public PlayingCard(String suit, String value) {
50            this.suit = SUITS.get(suit);
51            this.value = VALUES.get(value);
52        }
53
54        @Override
55        public int getValue() {
56            return value;
57        }
58
59        @Override
60        public String toString() {
61            return String.format("%s of %s", VALUE_NAMES.get(value), SUIT_NAMES.get(suit));
62        }
63    }
64
65    public static class Game {
66        private ArrayList<Card> cards;
67
68        public Game() {
69            cards = new ArrayList<>();
70        }
71
72        public void addCard(String suit, String value) {
73            cards.add(new PlayingCard(suit, value));
74        }
75
76        public String cardString(int card) {
77            return cards.get(card).toString();
78        }
79
80        public boolean cardBeats(int cardA, int cardB) {
81            return cards.get(cardA).compareTo(cards.get(cardB)) > 0;
82        }
83    }
84
85    public static void main(String[] args) {
86        Scanner scanner = new Scanner(System.in);
87        Game game = new Game();
88        String[] segs = scanner.nextLine().split(" ");
89        game.addCard(segs[0], segs[1]);
90        System.out.println(game.cardString(0));
91        segs = scanner.nextLine().split(" ");
92        game.addCard(segs[0], segs[1]);
93        System.out.println(game.cardString(1));
94        System.out.println(game.cardBeats(0, 1));
95        scanner.close();
96    }
97}
98

The Game class stores a list of cards which takes O(n) space where n is the number of cards added. Each method (add_card, card_string, card_beats) uses O(1) time and O(1) space.

Part Two

For this part, we ask you to implement the Jokers into the system.

In addition to the functionalities above, also implement the following functions:

  • add_joker(color): Creates a Joker card with color of either Red or Black.
    • Joker beats everything else except other jokers. This card is represented by i, where i is an integer indicating how many cards have been created before, including both normal cards and jokers.
    • A joker's string representation is Red Joker or Black Joker, depending on the color.

You may copy the code from the previous question here.

Try it yourself

Solution

We add a Joker class that inherits the base Card. For the purpose of this question, its value is 14, which is greater than other cards. We do not need to write extra logic for comparing Jokers with other cards, since that logic is already there under Card.

Below is the updated implementation:

1from enum import Enum, auto
2
3class Card:
4    @property
5    def card_value(self) -> int:
6        raise NotImplementedError()
7
8    def __lt__(self, other):
9        return self.card_value < other.card_value
10
11class Suit(Enum):
12    CLUBS = auto()
13    DIAMONDS = auto()
14    HEARTS = auto()
15    SPADES = auto()
16
17class PlayingCard(Card):
18    SUITS = {
19        "Clubs": Suit.CLUBS,
20        "Diamonds": Suit.DIAMONDS,
21        "Hearts": Suit.HEARTS,
22        "Spades": Suit.SPADES,
23    }
24    SUIT_NAMES = {e: n for n, e in SUITS.items()}
25    VALUES = {
26        "A": 1,
27        **{str(i): i for i in range(2, 11)},
28        "J": 11,
29        "Q": 12,
30        "K": 13,
31    }
32    VALUE_NAMES = {e: n for n, e in VALUES.items()}
33
34    def __init__(self, suit: str, value: str):
35        super().__init__()
36        self.__suit = self.SUITS[suit]
37        self.__value = self.VALUES[value]
38
39    @property
40    def card_value(self) -> int:
41        return self.__value
42
43    def __str__(self) -> str:
44        value = self.VALUE_NAMES[self.__value]
45        suit = self.SUIT_NAMES[self.__suit]
46        return f'{value} of {suit}'
47
48class JokerColor(Enum):
49    RED = auto()
50    BLACK = auto()
51
52class Joker(Card):
53    COLORS = {
54        "Red": JokerColor.RED,
55        "Black": JokerColor.BLACK,
56    }
57
58    COLOR_NAMES = {e: n for n, e in COLORS.items()}
59
60    def __init__(self, color: str):
61        super().__init__()
62        self.__color = self.COLORS[color]
63
64    @property
65    def card_value(self):
66        return 14
67
68    def __str__(self) -> str:
69        return f"{self.COLOR_NAMES[self.__color]} Joker"
70
71class Game:
72    def __init__(self):
73        self.__cards: list[Card] = []
74
75    def add_card(self, suit: str, value: str) -> None:
76        self.__cards.append(PlayingCard(suit, value))
77
78    def card_string(self, card: int) -> str:
79        return str(self.__cards[card])
80
81    def card_beats(self, card_a: int, card_b: int) -> bool:
82        return self.__cards[card_a] > self.__cards[card_b]
83
84    def add_joker(self, color: str) -> None:
85        self.__cards.append(Joker(color))
86
87if __name__ == '__main__':
88    game = Game()
89    suit, value = input().split()
90    game.add_joker(value) if suit == "Joker" else game.add_card(suit, value)
91    print(game.card_string(0))
92    suit, value = input().split()
93    game.add_joker(value) if suit == "Joker" else game.add_card(suit, value)
94    print(game.card_string(1))
95    print("true" if game.card_beats(0, 1) else "false")
96
1import java.util.ArrayList;
2import java.util.HashMap;
3import java.util.Map;
4import java.util.Scanner;
5import java.util.Map.Entry;
6import java.util.stream.Collectors;
7
8class Solution {
9    public static abstract class Card implements Comparable<Card> {
10        public abstract int getValue();
11
12        @Override
13        public int compareTo(Card o) {
14            return Integer.compare(getValue(), o.getValue());
15        }
16    }
17
18    public enum Suit {
19        SPADES, HEARTS, DIAMONDS, CLUBS
20    }
21
22    public static class PlayingCard extends Card {
23        private Suit suit;
24        private int value;
25
26        public static final Map<String, Suit> SUITS = Map.of(
27            "Spades", Suit.SPADES,
28            "Hearts", Suit.HEARTS,
29            "Diamonds", Suit.DIAMONDS,
30            "Clubs", Suit.CLUBS
31        );
32        // Inverts the above map to convert back to string.
33        public static final Map<Suit, String> SUIT_NAMES = SUITS.entrySet().stream().collect(Collectors.toMap(Map.Entry::getValue, Map.Entry::getKey));
34
35        // Map.of is limited to 10 entries, so we initialize a static map instead
36        public static final Map<String, Integer> VALUES = new HashMap<>();
37        static {
38            VALUES.put("A", 1);
39            for (int i = 2; i <= 10; i++) {
40                VALUES.put(String.valueOf(i), i);
41            }
42            VALUES.put("J", 11);
43            VALUES.put("Q", 12);
44            VALUES.put("K", 13);
45        }
46        // Inverts the above map to convert back to string.
47        public static final Map<Integer, String> VALUE_NAMES = VALUES.entrySet().stream().collect(Collectors.toMap(Map.Entry::getValue, Map.Entry::getKey));
48
49        public PlayingCard(String suit, String value) {
50            this.suit = SUITS.get(suit);
51            this.value = VALUES.get(value);
52        }
53
54        @Override
55        public int getValue() {
56            return value;
57        }
58
59        @Override
60        public String toString() {
61            return String.format("%s of %s", VALUE_NAMES.get(value), SUIT_NAMES.get(suit));
62        }
63    }
64
65    public enum JokerColor {
66        RED, BLACK
67    }
68
69    public static class Joker extends Card {
70        private JokerColor color;
71
72        public static final Map<String, JokerColor> COLORS = Map.of(
73            "Red", JokerColor.RED,
74            "Black", JokerColor.BLACK
75        );
76        // Inverts the above map to convert back to string.
77        public static final Map<JokerColor, String> COLOR_NAMES = COLORS.entrySet().stream().collect(Collectors.toMap(Map.Entry::getValue, Map.Entry::getKey));
78
79        public Joker(String color) {
80            this.color = COLORS.get(color);
81        }
82
83        @Override
84        public int getValue() {
85            return 14;
86        }
87
88        @Override
89        public String toString() {
90            return String.format("%s Joker", COLOR_NAMES.get(color));
91        }
92    }
93
94    public static class Game {
95        private ArrayList<Card> cards;
96
97        public Game() {
98            cards = new ArrayList<>();
99        }
100
101        public void addCard(String suit, String value) {
102            cards.add(new PlayingCard(suit, value));
103        }
104
105        public String cardString(int card) {
106            return cards.get(card).toString();
107        }
108
109        public boolean cardBeats(int cardA, int cardB) {
110            return cards.get(cardA).compareTo(cards.get(cardB)) > 0;
111        }
112
113        public void addJoker(String color) {
114            cards.add(new Joker(color));
115        }
116    }
117
118    public static void main(String[] args) {
119        Scanner scanner = new Scanner(System.in);
120        Game game = new Game();
121        String[] segs = scanner.nextLine().split(" ");
122        if (segs[0].equals("Joker"))
123            game.addJoker(segs[1]);
124        else
125            game.addCard(segs[0], segs[1]);
126        System.out.println(game.cardString(0));
127        segs = scanner.nextLine().split(" ");
128        if (segs[0].equals("Joker"))
129            game.addJoker(segs[1]);
130        else
131            game.addCard(segs[0], segs[1]);
132        System.out.println(game.cardString(1));
133        System.out.println(game.cardBeats(0, 1));
134        scanner.close();
135    }
136}
137

The method add_joker uses O(1) time and O(1) space.

Part Three

This game also involve a concept of a Hand and comparing the size of the two hands. For this part, add these following functions to the Game class:

  • add_hand(card_indices): Create a new Hand with cards represented by the list of integer representation of cards card_indices. The hand can be represented by i, where i is the number of hands added before.
  • hand_string(hand): Return the string representation of the hand represented by hand. It is a list of string representation of cards by their insertion order, separated by ", ". For example, if hand has a 9 of Clubs, K of Hearts, and a Black Joker, the string representation is "9 of Clubs, K of Hearts, Black Joker".
  • beats_hand(hand_a, hand_b): Check if the hand represented by hand_a beats the hand represented by hand_b according to the following rules:
    • Starting from the largest card in each hand, compare them. If a card beats another, that hand beats the other hand. Otherwise, compare the next largest card.
    • Repeat this process until one hand beats the other, or one hand runs out of cards. If a hand runs out of cards, neither hand beat each other.

Try it yourself

Solution

For this part, we implement the Hand class by having it contain a list of cards. When we compare two hands, because we defined a comparison function between two cards, we can sort them using the default sorting algorithm.

Below is the implementation:

1from enum import Enum, auto
2from typing import List
3
4class Card:
5    @property
6    def card_value(self) -> int:
7        raise NotImplementedError()
8
9    def __lt__(self, other):
10        return self.card_value < other.card_value
11
12class Suit(Enum):
13    CLUBS = auto()
14    DIAMONDS = auto()
15    HEARTS = auto()
16    SPADES = auto()
17
18class PlayingCard(Card):
19    SUITS = {
20        "Clubs": Suit.CLUBS,
21        "Diamonds": Suit.DIAMONDS,
22        "Hearts": Suit.HEARTS,
23        "Spades": Suit.SPADES,
24    }
25    SUIT_NAMES = {e: n for n, e in SUITS.items()}
26    VALUES = {
27        "A": 1,
28        **{str(i): i for i in range(2, 11)},
29        "J": 11,
30        "Q": 12,
31        "K": 13,
32    }
33    VALUE_NAMES = {e: n for n, e in VALUES.items()}
34
35    def __init__(self, suit: str, value: str):
36        super().__init__()
37        self.__suit = self.SUITS[suit]
38        self.__value = self.VALUES[value]
39
40    @property
41    def card_value(self) -> int:
42        return self.__value
43
44    def __str__(self) -> str:
45        value = self.VALUE_NAMES[self.__value]
46        suit = self.SUIT_NAMES[self.__suit]
47        return f'{value} of {suit}'
48
49class JokerColor(Enum):
50    RED = auto()
51    BLACK = auto()
52
53class Joker(Card):
54    COLORS = {
55        "Red": JokerColor.RED,
56        "Black": JokerColor.BLACK,
57    }
58
59    COLOR_NAMES = {e: n for n, e in COLORS.items()}
60
61    def __init__(self, color: str):
62        super().__init__()
63        self.__color = self.COLORS[color]
64
65    @property
66    def card_value(self):
67        return 14
68
69    def __str__(self) -> str:
70        return f"{self.COLOR_NAMES[self.__color]} Joker"
71
72class Hand:
73    def __init__(self, cards):
74        super().__init__()
75        self.cards = [*cards]
76
77    def __str__(self) -> str:
78        return ", ".join(str(card) for card in self.cards)
79
80    def __lt__(self, other):
81        for card_a, card_b in zip(reversed(sorted(self.cards)), reversed(sorted(other.cards))):
82            if card_a < card_b:
83                return True
84            elif card_b < card_a:
85                return False
86        return False