🧠 Guess Two‑Thirds Game – A Web3 Game of Strategy

This repository contains a decentralized implementation of the classic Guess Two‑Thirds of the Average game, running on the Ethereum blockchain.

Players join by sending any amount of ETH. When the round ends, the player whose contribution is closest to  2 / 3  of the average wins the entire prize pool (minus a 1 % owner fee).
The stop‑condition is pseudo‑random and parametrised on deployment, so the game designer can decide how quickly a round should finish (e.g. 2–3 players, 5–10 players, etc.).

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🎮 Game Rules

• Join by sending any positive amount of ETH.
• Each address may participate only once per round.
• When the round ends:
  1. Compute the average of all submitted amounts.
  2. Take 2 / 3  of that average as the target.
  3. The player whose amount is closest to the target wins.
  4. If there is a tie, the earliest participant wins.

🕹️ How the Game Ends

• At deployment you choose minX and maxX (both ≥ 1, minX ≤ maxX).
• For every new participant count n, the contract draws
  x ∈ [minX, maxX] using on‑chain randomness (block.prevrandao & block hash).
• The game cannot end before x players have joined.
• After that, another pseudo‑random draw decides whether the current n is the final count.
• With minX = 2, maxX = 3 (recommended for demos), a round typically ends within 6–9 players.

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📜 Smart Contract

Main file: contracts/GuessTwoThirdsGame.sol

Features:

• Player registration, payment handling, and “one‑address‑one‑entry” guard.
• Constructor GuessTwoThirdsGame(uint256 minX, uint256 maxX) sets the early‑stop range.
• Pseudo‑random end logic based on block.prevrandao and blockhash.
• Automatic prize/fee distribution (1 % fee to owner).
• Written in Solidity ^0.8.19 – uses OpenZeppelin’s ReentrancyGuard.

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🧪 Testing

This project uses [Hardhat] and [Ethers.js].

Run the full suite with:

npx hardhat test

Tests check:

• Single‑player participation
• Rejection of duplicate participation
• Round termination and winner determination under the new, quicker stop‑condition

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🚀 Deployment

Deploy with the Hardhat script, passing minX and maxX on the command line:

npx hardhat run --network <network-name> scripts/deploy.js <minX> <maxX>

Example (2–3 player threshold on Sepolia):

npx hardhat run --network sepolia scripts/deploy.js 2 3

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📂 Project Structure

guess-two-thirds-game/
│
├── contracts/
│   └── GuessTwoThirdsGame.sol     # Main game contract
│
├── test/
│   └── GuessTwoThirdsGame.js      # Mocha/Chai test suite
│
├── scripts/
│   └── deploy.js                  # Deployment script (takes minX, maxX)
│
├── hardhat.config.js              # Hardhat configuration
└── package.json                   # Dependencies and scripts

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📦 Dependencies

npm install --save-dev hardhat @nomicfoundation/hardhat-toolbox
npm install @openzeppelin/contracts

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🧠 Inspiration

The contract brings the classic experimental‑economics game “Guess 2 / 3 of the Average” to Web3, ensuring fairness through on‑chain pseudo‑randomness and public verifiability.

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🛡️ License

Distributed under the MIT License.