Renju Cat

Renju: A Competitive Board Game
(Classic Renju Rules – Modernized for Clarity and Fair Play)

🎮 Overview

Renju is a strategic, two-player abstract board game that originated in East Asia as a refined variant of Gomoku. It is played on a grid, where players take turns placing their markers with the goal of forming five in a row—but with additional rules to prevent unfair advantages and promote balanced, skillful gameplay.

🧩 Game Setup

• Board: 15×15 grid (standard size; can vary slightly in some versions).
• Players: Two players—Player 1 (X) and Player 2 (O).
• Markers: X and O (or colored stones in physical versions).
• First Move: Player X goes first.

⚠️ Important Note: Unlike basic Gomoku, Renju includes opening rules and forbidden moves to prevent an immediate win by the first player.

📌 Core Objective

Be the first player to form an unbroken line of exactly five of your markers, either:

• Horizontally (left to right),
• Vertically (top to bottom),
• Diagonally (up-left to down-right or down-left to up-right).

❌ Note: More than five in a row does not count as a win. The line must be exactly five.

🛑 Key Renju Rules (Enforced for Fair Play)

1. Opening Rule – "First Move Advantage"

• Player X makes the first move and places one stone anywhere on the board.
• Player O responds with two moves (placing two O stones) on their turn.

🔁 Purpose: Prevents Player X from easily forcing a win by symmetry.

2. Forbidden Moves (Prohibited Patterns)

To avoid trivial wins, certain patterns are illegal for either player to create. The most important are:

• Double Three (Forbidden):
  A player may not create two separate lines of exactly three stones (e.g., three in a row and another three in a different direction), unless both are blocked at both ends.

• Winning in a Single Move (Prevention):
  A player cannot legally win by placing a stone that completes more than one line of five at once (double win).

  ❌ Exception: This is allowed only if the player has not already created a winning pattern earlier.

• Four in a Row (Unblocked):
  A player may not place a stone to create four in a row with both ends open, unless the move is part of a forced winning sequence (forbidden under "overline" rules).

✅ Rule of Thumb: Players must avoid creating "unblocked" lines of four or five unless they are the winning move.

3. Win Conditions

• A player wins only by completing exactly five in a row, with no more than five in that line.
• Blocking the opponent’s potential five-in-a-row is key.
• Draws are rare but possible if the board fills and no one achieves five in a row.

🔄 Gameplay Flow

1. Player X places one X on the board (any empty intersection).
2. Player O places two O stones on the board (on separate, empty intersections).
3. Players alternate turns:
   • Each turn, a player places one of their markers on an empty cell.
   • Players must follow the forbidden move rules.
4. The game ends when:
   • One player forms five in a row → Win.
   • The board fills completely and no one has five in a row → Draw.

🏆 Winning Example

    X X X X X

→ Win for X (five horizontal).

    X
    X
    X
    X
    X

→ Win for X (five vertical).

    X
      X
        X
          X
            X

→ Win for X (diagonal).

✅ All these are valid wins only if no extra stones are in the line.

🧠 Strategy Tips

• Control the center: The center of the board offers the most opportunities for multiple lines.
• Block early: Prevent the opponent from building 3s or 4s.
• Use symmetry wisely: Avoid creating patterns that allow your opponent to mirror and win.
• Watch for double threats: Set up two winning lines simultaneously to force a win.

📝 Summary: Renju vs Gomoku

✅ Final Note

Renju is not just a game of luck or brute force—it rewards deep strategy, foresight, and pattern recognition. With its rich ruleset, Renju remains a popular competitive game in tournaments and online platforms like Renju.net and Lichess.

🏁 Winner: The first player to form exactly five in a row—horizontally, vertically, or diagonally—wins the game.

🎮 Ready to play? Place your first stone—and may the best strategist win!