Designing a Tic Tac Toe Game
What is the Tic Tac Toe Problem?
Section titled “What is the Tic Tac Toe Problem?”Design a Tic Tac Toe game that allows two players to play on a 3x3 grid. Players take turns placing their symbols (X or O) in empty cells. The game should detect wins (three in a row horizontally, vertically, or diagonally) and handle draws when all cells are filled.
In this problem, you’ll design a system that manages player turns, validates moves on a shared board, and identifies the exact moment a player wins or the game ends in a draw.
Problem Overview
Section titled “Problem Overview”Design a two-player game played on a 3x3 grid where players alternate placing their symbols (X and O) until one wins or the board is full.
Core Requirements
Section titled “Core Requirements”Functional Requirements:
- Standard Grid: Play on a classic 3x3 board.
- Two Players: Support two players taking turns with ‘X’ and ‘O’ symbols.
- Win Detection: Identify when a player has three symbols in a row (horizontal, vertical, or diagonal).
- Draw Handling: Detect when all cells are filled without a winner.
- Move Validation: Reject invalid moves (e.g., occupied cells) and notify the player.
- Scoreboard: Keep track of scores/wins across multiple games.
- Demo Mode: Support predefined moves for flow demonstration.
Non-Functional Requirements:
- Object-Oriented Design: Clear separation between Game, Board, Cell, and Player.
- Modularity: Easy to extend for larger boards (N x N) or AI opponents.
- Testability: Core game logic should be easy to understand and unit test.
- Readable Output: Display the current state of the board clearly after each move.
What’s Expected?
Section titled “What’s Expected?”1. System Architecture
Section titled “1. System Architecture”The system coordinates between the Game controller, the Board, and the Players.
2. Key Classes to Design
Section titled “2. Key Classes to Design”classDiagram
class Game {
-Board board
-Player[] players
-int turn
-GameStatus status
+makeMove(row, col)
+checkWinner()
}
class Board {
-Cell[][] grid
-int size
+isFull()
+setCellValue(row, col, symbol)
}
class Player {
-String name
-Symbol symbol
}
Game --> Board
Game o-- Player
Board *-- Cell
System Flow
Section titled “System Flow”Move and Win Detection Flow
Section titled “Move and Win Detection Flow”
Key Design Challenges
Section titled “Key Design Challenges”1. Efficient Win Detection
Section titled “1. Efficient Win Detection”Checking every row, column, and diagonal after every move (using nested loops) is $O(N^2)$. While fine for 3x3, it’s inefficient for 1000x1000.
Solution: Use Counter-based tracking. Maintain arrays rows[] and cols[] and two variables for diagonals. When a player moves at (r, c), increment the count for that row and column. If the count reaches $N$, you have a winner. This reduces detection to $O(1)$.
2. Abstracting the Board
Section titled “2. Abstracting the Board”The game logic should not be tied to a fixed 3x3 array.
Solution: Encapsulate the grid in a Board class. Provide methods like isValidMove(r, c) and setCellValue(r, c, val). This allows you to change the underlying storage (e.g., from a 2D array to a Map for sparse boards) without affecting the Game controller.
3. Handling Player Symbols
Section titled “3. Handling Player Symbols”Hardcoding ‘X’ and ‘O’ in the logic makes it hard to support more players or custom symbols.
Solution: Use an Enum or a Player Class. The game logic should check if player.getSymbol() matches across a row, rather than checking specifically for the character ‘X’.
What You’ll Learn
Section titled “What You’ll Learn”By solving this problem, you’ll master:
- ✅ State Management - Handling game lifecycles and transitions.
- ✅ Algorithmic Optimization - Turning $O(N^2)$ checks into $O(1)$ updates.
- ✅ Grid Logic - Modeling and traversing 2D spatial structures.
- ✅ Clean Code - Separating rule enforcement from data representation.
View Complete Solution & Practice
Section titled “View Complete Solution & Practice”Ready to see the full implementation? Open the interactive playground to access:
- 🎯 Step-by-step guidance through the 8-step LLD approach
- 📊 Interactive UML builder to visualize your design
- 💻 Complete Code Solutions in Python, Java, C++, TypeScript, JavaScript, C#
- 🤖 AI-powered review of your design and code
Related Problems
Section titled “Related Problems”After mastering Tic Tac Toe, try these similar problems:
- Chess Game - Much more complex move rules and piece logic.
- Snake and Ladder - Board game with randomized movement and state.
- Connect Four - Similar grid logic with gravity-based moves.