How to design Snake and Ladder?

1.	How to design Snake and Ladder?
Answer» Here is how the "Snake and Ladder problem" can be solved by using the above approach. 1. Gathering Requirements: Create a multiplayer Snake and Ladder game in such a way that the game should take input N from the user at the start of the game to create a board of size N x N. The board should have some snakes and ladders placed randomly in such a way the snake will have its head position at a higher number than the tail and ladder will have start position at smaller number than END position. Also, No ladder and snake create a cycle and no snake tail position has a ladder start position & vice versa. The players take their turn one after another and during their turn, they roll the dice to get a random number and the player has to move forward that many positions. If the player ends up at a cell with the head of the snake, the player has to be punished and should go down to the cell that CONTAINS the tail of the same snake & If the player ends up at a cell with the start position of a ladder, the player has to be rewarded and should climb the ladder to reach the cell which has a top position of the ladder. Initially, each player is outside of the board (at position 0). If at any point of time, the player has to move outside of the board (say player at position 99 on a 100 cell board and dice rolls give 4) the player stays at the same position. Possible future extension: The game can be played by more than one dice. (i.e. if there are two dices then the numbers from 2 to 12 will be generated). On getting a 6, you get another turn and on getting 3 consecutive 6s, all three of those get cancelled. 2. Class Diagram & Use Case Diagram: 3. Code IMPLEMENTATION: Driver.java package snakeLadder; public class Driver { public static void main(String[] args) { SpecialEntity snake1 = new Snake(12, 28); SpecialEntity snake2 = new Snake(34, 78); SpecialEntity snake3 = new Snake(6, 69); SpecialEntity snake4 = new Snake(65, 84); SpecialEntity ladder1 = new Ladder(24, 56); SpecialEntity ladder2 = new Ladder(43, 83); SpecialEntity ladder3 = new Ladder(3, 31); SpecialEntity ladder4 = new Ladder(72, 91); Board board = new Board(10); board.addSpecialEntity(snake1); board.addSpecialEntity(snake2); board.addSpecialEntity(snake3); board.addSpecialEntity(snake4) board.addSpecialEntity(ladder1); board.addSpecialEntity(ladder2); board.addSpecialEntity(ladder3); board.addSpecialEntity(ladder4); Dice dice = new Dice(6); Game game = new Game(board, dice); Player player1 = new Player("p1"); Player player2 = new Player("P2"); Player player3 = new Player("p3"); players = List<Player>(){player1, player2, player3}; game.addPlayers(players); game.launch(); } } Game.java package snakeLadder; import snakeLadder.GameStatus;import snakeLadder.Player;import snakeLadder.Dice;import snakeLadder.Board; import java.util.Queue;import java.util.Scanner;import java.util.LinkedList; public class Game { Board board; Dice dice; Queue<Player> players; GameStatus staus; public Game(Board board, Dice dice) { this.board = board; this.dice = dice; this.players = new LinkedList<Player>(); this.status = GameStatus.NOT_STARTED; } public void startGame() { this.status = GameStatus.RUNNING; board.printBoard(); // Run until we have only 1 player left on the board while(players.size() > 1) { Player player = players.poll(); makeMove(currPlayer); if(player.getPosition() == board.getTotalCells()) System.out.println(player.getName() + " has completed the game!"); else players.add(player); } this.status = GameStatus.FINISHED; } private void makeMove(Player player) { System.out.println(); System.out.println(currPlayer.getUserName()+"'s turn."); System.out.println("Press anything to roll the dice."); Scanner sc = new Scanner(System.in); char C = sc.next().charAt(0); int playerPosition = player.getPosition(); int rollValue = dice.roll(); int targetPosition = playerPosition + rollValue; if(targetPosition > board.getTotalCells()) System.out.println("Invalid Move"); else { if(board.hasSpecialEntity(targetPosition)) { targetPosition = board.getSpecialEntity(targetPosition).getEndPosition(); } } player.setPosition(targetPosition); } public void addPlayers(List<Player> all_players) { if(this.status == GameStatus.NOT_STARTED) { for(Player player : all_players) this.players.add(player); } else throw new GameAlreadyStartedException("Can't add players after game started") } } Board.java package snakeLadder; import lombok.Getter; public class Board{ @Getter int dimension; HashMap<Integer, SpecialEntity> specialEntities; public Board(int dimension) { this.dimension = dimension; } public void printBoard() { int totalCells = dimensiondimension; for(int i=totalCells; i > 0; i--) { System.out.print(" \| " + i + " ") if(hasSpecialEntity(i)) System.out.print(specialEntities.get(i).getID()); System.out.print(" \|"); if(totalCells % 10 == 0) System.out.println(); } } public int getTotalCells() { return this.dimesion this.dimesion; } public void addSpecialEntity(SpecialEntity entity) { int actionPosition = entity.getActionPosition(); specialEntities.put(actionPosition, entity); } public boolean hasSpecialEntity(int position) { return specialEntities.containsKey(position); } public SpecialEntity getSpecialEntity(int position) { if(hasSpecialEntity(position)) return specialEntities.get(position); return null; }} Dice.java package snakeLadder; import lombok.Getter; public class Dice{ int maxValue; public Dice(int maxVal) { this.maxValue = maxVal; } public int roll() { return (int) Math.floor(Math.random()*maxValue + 1); }} GameStatus.java package snakeLadder; public enum GameStatus { NOT_STARTED, RUNNING, FINISHED} SpecialEntity.java package snakeLadder; import lombok.Getter;public abstract class BoardEntity { private int start; private int end; public SpecialEntity(int start, int end) { this.start = start; this.end = end; } public abstract String getID(); public int getActionPosition() { return this.start; } public int getEndPosition() { return this.end; }} Snake.java package snakeLadder; public class Snake extends SpecialEntity{ public Snake(int start, int end) { super(start, end); } @Override public String getID() { return "S_"+ this.getEnd(); } } Ladder.java package snakeLadder; public class Ladder extends SpecialEntity{ public Ladder(int start, int end) { super(start, end); } @Override public String getID() { return "L_"+ this.getEnd(); } } Player.java package snakeLadder; import lombok.Getter;import lombok.Setter; public class Player{ @Getter @Setter int position; @Getter String name; public Player(String name) { this.name = name; this.position = 0; }} GameAlreadyStartedException.java package snakeLadder; public class GameAlreadyStartedException extends Exception { public GameAlreadyStartedException(String message) { super(message); }} It is important to structure the code into different classes with each class having a single responsibility (Remember S in SOLID Principles) and also having relations between the classes so that they can be easily extensible. Some frequently asked low-level design examples to practice are: Design Parking Lot Design Splitwise Design Tik Tok Toe Game Design Car Rental System Design Bookmyshow Design Pub Sub System Design Coffee Vending Machine

Answer»

Here is how the "Snake and Ladder problem" can be solved by using the above approach.

1. Gathering Requirements: Create a multiplayer Snake and Ladder game in such a way that the game should take input N from the user at the start of the game to create a board of size N x N. The board should have some snakes and ladders placed randomly in such a way the snake will have its head position at a higher number than the tail and ladder will have start position at smaller number than END position. Also, No ladder and snake create a cycle and no snake tail position has a ladder start position & vice versa.

The players take their turn one after another and during their turn, they roll the dice to get a random number and the player has to move forward that many positions. If the player ends up at a cell with the head of the snake, the player has to be punished and should go down to the cell that CONTAINS the tail of the same snake & If the player ends up at a cell with the start position of a ladder, the player has to be rewarded and should climb the ladder to reach the cell which has a top position of the ladder. Initially, each player is outside of the board (at position 0). If at any point of time, the player has to move outside of the board (say player at position 99 on a 100 cell board and dice rolls give 4) the player stays at the same position.

Possible future extension:

The game can be played by more than one dice. (i.e. if there are two dices then the numbers from 2 to 12 will be generated).
On getting a 6, you get another turn and on getting 3 consecutive 6s, all three of those get cancelled.

2. Class Diagram & Use Case Diagram:

3. Code IMPLEMENTATION:

Driver.java

package snakeLadder; public class Driver { public static void main(String[] args) { SpecialEntity snake1 = new Snake(12, 28); SpecialEntity snake2 = new Snake(34, 78); SpecialEntity snake3 = new Snake(6, 69); SpecialEntity snake4 = new Snake(65, 84); SpecialEntity ladder1 = new Ladder(24, 56); SpecialEntity ladder2 = new Ladder(43, 83); SpecialEntity ladder3 = new Ladder(3, 31); SpecialEntity ladder4 = new Ladder(72, 91); Board board = new Board(10); board.addSpecialEntity(snake1); board.addSpecialEntity(snake2); board.addSpecialEntity(snake3); board.addSpecialEntity(snake4) board.addSpecialEntity(ladder1); board.addSpecialEntity(ladder2); board.addSpecialEntity(ladder3); board.addSpecialEntity(ladder4); Dice dice = new Dice(6); Game game = new Game(board, dice); Player player1 = new Player("p1"); Player player2 = new Player("P2"); Player player3 = new Player("p3"); players = List<Player>(){player1, player2, player3}; game.addPlayers(players); game.launch(); } }

Game.java

package snakeLadder; import snakeLadder.GameStatus;import snakeLadder.Player;import snakeLadder.Dice;import snakeLadder.Board; import java.util.Queue;import java.util.Scanner;import java.util.LinkedList; public class Game { Board board; Dice dice; Queue<Player> players; GameStatus staus; public Game(Board board, Dice dice) { this.board = board; this.dice = dice; this.players = new LinkedList<Player>(); this.status = GameStatus.NOT_STARTED; } public void startGame() { this.status = GameStatus.RUNNING; board.printBoard(); // Run until we have only 1 player left on the board while(players.size() > 1) { Player player = players.poll(); makeMove(currPlayer); if(player.getPosition() == board.getTotalCells()) System.out.println(player.getName() + " has completed the game!"); else players.add(player); } this.status = GameStatus.FINISHED; } private void makeMove(Player player) { System.out.println(); System.out.println(currPlayer.getUserName()+"'s turn."); System.out.println("Press anything to roll the dice."); Scanner sc = new Scanner(System.in); char C = sc.next().charAt(0); int playerPosition = player.getPosition(); int rollValue = dice.roll(); int targetPosition = playerPosition + rollValue; if(targetPosition > board.getTotalCells()) System.out.println("Invalid Move"); else { if(board.hasSpecialEntity(targetPosition)) { targetPosition = board.getSpecialEntity(targetPosition).getEndPosition(); } } player.setPosition(targetPosition); } public void addPlayers(List<Player> all_players) { if(this.status == GameStatus.NOT_STARTED) { for(Player player : all_players) this.players.add(player); } else throw new GameAlreadyStartedException("Can't add players after game started") } }

Board.java

package snakeLadder; import lombok.Getter; public class Board{ @Getter int dimension; HashMap<Integer, SpecialEntity> specialEntities; public Board(int dimension) { this.dimension = dimension; } public void printBoard() { int totalCells = dimension*dimension; for(int i=totalCells; i > 0; i--) { System.out.print(" | " + i + " ") if(hasSpecialEntity(i)) System.out.print(specialEntities.get(i).getID()); System.out.print(" |"); if(totalCells % 10 == 0) System.out.println(); } } public int getTotalCells() { return this.dimesion * this.dimesion; } public void addSpecialEntity(SpecialEntity entity) { int actionPosition = entity.getActionPosition(); specialEntities.put(actionPosition, entity); } public boolean hasSpecialEntity(int position) { return specialEntities.containsKey(position); } public SpecialEntity getSpecialEntity(int position) { if(hasSpecialEntity(position)) return specialEntities.get(position); return null; }}

Dice.java

package snakeLadder; import lombok.Getter; public class Dice{ int maxValue; public Dice(int maxVal) { this.maxValue = maxVal; } public int roll() { return (int) Math.floor(Math.random()*maxValue + 1); }}

GameStatus.java

package snakeLadder; public enum GameStatus { NOT_STARTED, RUNNING, FINISHED}

SpecialEntity.java

package snakeLadder; import lombok.Getter;public abstract class BoardEntity { private int start; private int end; public SpecialEntity(int start, int end) { this.start = start; this.end = end; } public abstract String getID(); public int getActionPosition() { return this.start; } public int getEndPosition() { return this.end; }}

Snake.java

package snakeLadder; public class Snake extends SpecialEntity{ public Snake(int start, int end) { super(start, end); } @Override public String getID() { return "S_"+ this.getEnd(); } }

Ladder.java

package snakeLadder; public class Ladder extends SpecialEntity{ public Ladder(int start, int end) { super(start, end); } @Override public String getID() { return "L_"+ this.getEnd(); } }

Player.java

package snakeLadder; import lombok.Getter;import lombok.Setter; public class Player{ @Getter @Setter int position; @Getter String name; public Player(String name) { this.name = name; this.position = 0; }}

GameAlreadyStartedException.java

package snakeLadder; public class GameAlreadyStartedException extends Exception { public GameAlreadyStartedException(String message) { super(message); }}

It is important to structure the code into different classes with each class having a single responsibility (Remember S in SOLID Principles) and also having relations between the classes so that they can be easily extensible.

Some frequently asked low-level design examples to practice are:

Design Parking Lot
Design Splitwise
Design Tik Tok Toe Game
Design Car Rental System
Design Bookmyshow
Design Pub Sub System
Design Coffee Vending Machine

How to design Snake and Ladder?

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