What is Connect 4 Algorithm Design?

Connect 4 algorithm design is about creating the game logic - the rules, win detection, and player management that make the game work. This means:

How pieces fall into the lowest available position
Detecting when a player connects four pieces in a row
Managing player turns and game state
Validating moves before they happen

The Big Picture: Algorithms are the step-by-step instructions that make games fair, fun, and functional.

Algorithm Flow Overview

Before diving into the details, let's see the complete Connect 4 algorithm flow:

The Algorithm Stack: Data Structures, Logic, Validation

Data Structure: The Game Board

The board is a 2D array that represents our playing field:

// 2D array structure tells us what's in each position
let board = [
    [null, null, null, null, null, null, null], // Row 0 (top)
    [null, null, null, null, null, null, null], // Row 1
    [null, null, null, null, null, null, null], // Row 2
    [null, null, null, null, null, null, null], // Row 3
    [null, null, null, null, null, null, null], // Row 4
    [null, null, 'red', null, null, null, null]  // Row 5 (bottom)
];

Key Principle: Arrays create the foundation. Each position can hold null (empty), 'red', or 'yellow'.

Algorithm 1: Finding the Drop Position

function getDropRow(board, col) {
    // Start from bottom and work up
    for (let row = 5; row >= 0; row--) {
        if (board[row][col] === null) {
            return row; // Found empty spot
        }
    }
    return -1; // Column is full
}

Key Principle: Gravity simulation - pieces always fall to the lowest available position.

Try It Yourself

Click a column to see where the piece would fall:

Algorithm 2: Win Detection Logic

function checkWin(board, row, col) {
    const color = board[row][col];
    const directions = [
        [1, 0],   // vertical ↓
        [0, 1],   // horizontal →
        [1, 1],   // diagonal ↘
        [1, -1]   // diagonal ↙
    ];
    for (const [deltaRow, deltaCol] of directions) {
        let count = 1; // count current piece
        
        // Check both directions from current piece
        for (const direction of [-1, 1]) {
            let r = row + deltaRow * direction;
            let c = col + deltaCol * direction;
            
            while (r >= 0 && r < 6 && c >= 0 && c < 7 && 
                   board[r][c] === color) {
                count++;
                r += deltaRow * direction;
                c += deltaCol * direction;
            }
        }
        
        if (count >= 4) return true;
    }
    return false;
}

Key Concepts: Direction vectors, boundary checking, pattern matching

Core Algorithm Skills You'll Learn

Skill 1: State Management

Learning Goal: Keep track of game data and player turns

Try It Yourself

Current Player: Red

// State management connects all pieces together
class GameState {
    constructor() {
        this.board = this.createEmptyBoard();
        this.currentPlayer = 'red';
        this.gameOver = false;
    }
    
    makeMove(col) {
        const row = this.getDropRow(col);
        if (row >= 0) {
            this.board[row][col] = this.currentPlayer;
            
            if (this.checkWin(row, col)) {
                this.gameOver = true;
                return `${this.currentPlayer} wins!`;
            }
            
            this.switchPlayer();
        }
        return null;
    }
}

Skill 2: Win Detection in Action

Learning Goal: Detect four-in-a-row patterns immediately after each move

Try to Win!

Current Player: Red

Why This Matters: The game must instantly recognize victory conditions and end appropriately.

Quick Check

What's the most important concept you learned about Connect 4 algorithms?

What You Just Learned

Skill 1: Using 2D arrays to represent game boards
Skill 2: Implementing gravity with bottom-up searching
Skill 3: Detecting patterns using direction vectors

Key Takeaways

Data Structures Matter: 2D arrays perfectly model grid-based games
Algorithm Efficiency: Check wins only after moves, not constantly
Edge Cases: Always validate bounds and handle full columns
State Management: Keep track of whose turn it is and game status
Pattern Recognition: Use mathematical approaches to detect wins

Related Resources

MDN: JavaScript Arrays
Algorithm Design Manual
Game Programming Patterns

Duration: ~60 minutes | Audience: CS students learning algorithms | Meta-Goal: Understanding game logic through hands-on interaction