About

This tool is a high-fidelity implementation of the classic "Four-in-a-Row" strategy game, engineered for both casual play and algorithmic analysis. Unlike standard browser games, this engine utilizes 64-bit Bitboards (using JavaScript BigInt) to represent the game state, allowing for ultra-fast win detection and AI calculation speeds surpassing 20,000 nodes per second on standard hardware.

The core solver employs a Minimax Algorithm with Alpha-Beta Pruning and Iterative Deepening. This allows the AI to look ahead up to 10 plies (moves) into the future, evaluating positions based on material advantage, center control, and threats. The application also features a real-time Win Probability gauge, visualizing the engine's confidence in the current board state.

Note: Connect Four is a "solved game". With perfect play, the first player (Red) can always force a win. This engine approximates perfect play within the browser's execution time limits.

Formulas

The engine uses bitwise operations for instant win detection. A board state is mapped to a bitmask. For a board with R rows and C columns, we check for wins using bit shifts:

Horizontal Win Check:
m = pos & (pos >> 7)
IF (m & (m >> 14)) != 0 → TRUE

Heuristic Scoring Function:
Score(S) = ∑lines (w₄×N₄ + w₃×N₃ + w₂×N₂)

Where N_k is the count of k-length chains open on at least one side.

Reference Data

Dimension	Value	Description
Grid Size	7 × 6	Standard 7 columns, 6 rows layout.
State Space	4.5 × 10¹²	Total number of legal positions (approx 4.5 trillion).
Perfect Game	41 Moves	Maximum length of a game with optimal play on both sides.
First Player	Advantage	Mathematically proven win for Player 1 (Red).
Algorithm	Minimax	Recursive decision rule used for AI.
Heuristic	α-β Pruning	Optimization to eliminate irrelevant search branches.
Bitboard	64-bit	State storage using binary integers for O(1) ops.

Frequently Asked Questions

The AI is processing thousands of potential future board states. A visual delay (500ms) is also artificially added to make the opponent feel more "human" and allow you to see the move happen.

It visualizes the AI's evaluation of the current position. A full Red bar means the engine calculates a forced win for Red. A balanced bar indicates a draw or uncertain outcome.

Yes, but it requires near-perfect play. The Hard mode searches 8-10 moves ahead. Any mistake will be exploited immediately.

Undo reverts the board state and the internal random seed. If playing against AI, it undoes the last two moves (yours and the AI's) to restore your turn.