Connect Four Solver

Cross-platform desktop app to play and analyze Connect Four. Comes with a fast AI powered by minimax and alpha–beta pruning, a clean GUI, and helpful hints about forced wins.

Quick look

    

Features

• Play vs. AI or watch AI move: Choose who goes first on a simple setup screen.
• Strong search: Minimax with alpha–beta pruning and a small transposition table speeds up analysis.
• Smarter move ordering: Searches center columns first to prune more effectively and play more human-like moves.
• Immediate-win checks: Detects mate-in-1 for the side to move and avoids root-level blunders that allow an immediate reply win.
• Heuristic evaluation: Scores lines of four based on counts (2/3 in a row with empties) and emphasizes center control.
• Polished UI: Modern dark theme, 3D disc effects, responsive window resizing, and clear status indicators.
• Non-blocking AI: Calculation runs on a background thread, keeping the UI responsive and animations smooth.
• Forced-win indicator: When applicable, clearly warns "AI detects forced win in N turns."

How it works (high level)

• Game model: A Board tracks a 7×6 grid, current player, legal moves, wins/draws, and applies moves.
• Search: The Solver runs minimax with alpha–beta pruning. It caches (position, depth) results in a HashMap to avoid recomputation.
• Ordering: Candidate columns are ordered center-out to improve pruning and play strength.
• Tactics: Before full search, it checks for immediate winning moves; at the root it filters out moves that allow the opponent an instant win.
• Evaluation: For non-terminal nodes, a heuristic sums all 4-cell windows, rewarding threats (2/3 in a row with empties) and center occupancy; terminal wins/losses get large scores.
• Threading: AI move calculation is offloaded to a separate thread to prevent UI freezing.
• Depth: Default search depth is 9 plies; adjust in src/app.rs if you want a faster or stronger AI.

Build and run

• Requirements: Latest stable Rust toolchain.
• Build:

cargo build

• Run:

cargo run

Controls

• Setup: Pick who moves first (Human or AI).
• Play: Click a column to drop a piece.
• New Game returns to setup; Reset Board clears the current board.

Notes

• On Windows, if icon.ico exists, it will be embedded; otherwise a transparent placeholder is used.
• On macOS, the .app icon is provided via bundling metadata; the runtime uses a default icon.

Tech

• Rust, egui/eframe for the native GUI
• env_logger + log for simple logging