Design Snake and Ladder Game

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What is the Snake and Ladder Problem?

Design a Snake and Ladder game that allows multiple players to play on a standard 10×10 board (100 squares) with configurable snakes and ladders. Players take turns in round-robin order, rolling a simulated die (1-6) and moving their pieces. Rolling a 6 grants an extra turn. The game should handle snake bites (moving down) and ladder climbs (moving up), detect when a player wins (lands exactly on square 100), and allow multiple players to occupy the same square.

In this problem, you’ll design a system that supports multiple players, configurable board entities, and a robust game loop that identifies a winner with precision.

Why This Problem?

Snake and Ladder is an excellent LLD case study for:

• Inheritance - Abstracting “Board Entities” (Snakes, Ladders) into a common hierarchy.
• Queue-based Turn Management - Ensuring players take turns in a specific order.
• State Management - Tracking whether the game is Running or Finished.
• Modularity - Decoupling the Dice logic from the Game Controller.

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Problem Overview

Design a game played on a $10 \times 10$ board where players move from square 1 to 100 based on dice rolls, while navigating obstacles (snakes) and shortcuts (ladders).

Core Requirements

Functional Requirements:

• Board Setup: Initialize a 100-square grid with configurable snakes and ladders.
• Turn Logic: Support 2+ players taking turns in a fixed sequence.
• Dice Mechanics: Simulate a 1-6 die roll. A roll of ‘6’ grants an extra turn.
• Movement Rules: Handle snake bites (move down) and ladder climbs (move up).
• Winning Condition: A player wins by landing exactly on square 100.
• Multiple Occupancy: Allow any number of players on the same square.

Non-Functional Requirements:

• Extensibility: Allow changing board size or adding new entities easily.
• Clean Output: Provide a clear log of moves and game events.
• Robustness: Prevent invalid moves (e.g., rolling a 5 at square 98).

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What’s Expected?

1. System Architecture

The system coordinates between the Game controller, the Board, the Dice, and the Players.

2. Key Classes to Design

classDiagram
    class Game {
        -Board board
        -Dice dice
        -Queue~Player~ players
        -GameStatus status
        +play()
        -takeTurn(player)
    }
    
    class Board {
        -int size
        -Map~int, BoardEntity~ entities
        +getFinalPosition(pos)
    }
    
    class BoardEntity {
        <<abstract>>
        -int start
        -int end
        +action(pos)*
    }

    class Snake {
        +action()
    }

    class Player {
        -String name
        -int currentPos
    }

    Game --> Board
    Game --> Dice
    Board *-- BoardEntity
    BoardEntity <|-- Snake
    BoardEntity <|-- Ladder

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System Flow

Player Movement Flow

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Key Design Challenges

1. Encapsulating Board Obstacles

Snakes and ladders are essentially the same: they take you from $A$ to $B$. One goes up, one goes down.

Solution: Use Inheritance. Create an abstract BoardEntity class with start and end fields. Snake and Ladder inherit from this. The Board can then store a Map<Integer, BoardEntity>, allowing for $O(1)$ lookups to see if a square has an obstacle.

2. Round-Robin Turn Order

Managing who goes next can be tricky, especially when a ‘6’ grants an extra turn.

Solution: Use a Queue Data Structure. The Game class stores players in a queue. Every turn, you poll() the player, process their move, and then add() them back to the end of the queue. If they roll a ‘6’, you just process another turn before re-queuing them.

3. The Exact-100 Rule

A player must land exactly on 100. If they are at 98 and roll a 5, they should not move.

Solution: Implement Boundary Validation in the movement logic. Before updating the player’s currentPos, calculate the potential newPos. If newPos > board.size, return the original position, effectively skipping the movement part of the turn.

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What You’ll Learn

By solving this problem, you’ll master:

• ✅ Queue-based Logic - Managing sequential access to resources.
• ✅ State Transitions - Handling game phases and win conditions.
• ✅ OOP Abstraction - Using inheritance to simplify complex entities.
• ✅ Randomization Handling - Decoupling core logic from stochastic inputs.

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Related Problems

After mastering Snake and Ladder, try these similar problems:

• Tic-Tac-Toe - Simpler grid-based game state.
• Chess Game - Advanced piece logic and move validation.
• Elevator System - Managing queues and state transitions.