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| from abc import ABC | |
| import gymnasium as gym | |
| from gymnasium import spaces | |
| import numpy as np | |
| class NimGameEnv(gym.Env, ABC): | |
| """Custom environment for a simple Nim game. | |
| In this game, there are two players and a number of piles of stones. | |
| Each turn, a player can choose a pile and remove any number of stones from it. | |
| The player who takes the last stone loses. | |
| The observation space is a tuple of integers representing the number of stones in each pile. | |
| The action space is a tuple of two integers, representing the chosen pile and the number of stones to remove. | |
| """ | |
| def __init__(self, starting_stick_piles=[3, 5, 7]): | |
| self.starting_stick_piles = starting_stick_piles | |
| self.num_piles = len(starting_stick_piles) | |
| self.max_stones = max(starting_stick_piles) | |
| self.piles = self._init_piles() | |
| self.current_player = 0 | |
| self.action_space = spaces.MultiDiscrete([self.num_piles, self.max_stones + 1]) | |
| self.observation_space = spaces.MultiDiscrete([self.max_stones + 1] * self.num_piles) | |
| def step(self, action): | |
| """Take a step in the environment. | |
| Parameters | |
| ---------- | |
| action: tuple | |
| The action taken by the player, represented as a tuple of the chosen pile and the number of stones to remove. | |
| Returns | |
| ------- | |
| observation: tuple | |
| The current number of stones in each pile. | |
| reward: float | |
| The reward for the current step. | |
| done: bool | |
| Whether the game has ended. | |
| info: dict | |
| Additional information about the step. | |
| """ | |
| # Validate the action | |
| if not self._is_valid_action(action): | |
| raise ValueError("Invalid action") | |
| # Update the piles | |
| pile, num_stones = action | |
| self.piles[pile] -= num_stones | |
| # Determine if the game has ended | |
| done = self._is_game_over() | |
| # Calculate the reward | |
| reward = self._calculate_reward() | |
| # Switch the current player | |
| self.current_player = (self.current_player + 1) % 2 | |
| return self.piles, reward, done, {} | |
| def reset(self): | |
| """Reset the environment to the initial state.""" | |
| self.piles = self._init_piles() | |
| self.current_player = 0 | |
| text_observation = "The piles contain " + ", ".join(str(x) for x in self.piles) + " sticks." | |
| return text_observation, self.piles | |
| def _init_piles(self): | |
| """Initialize the stick piles.""" | |
| return [3, 5, 7] | |
| def _generate_random_stones(self): | |
| """Generate a random number of stones (between 1 and max_stones inclusive).""" | |
| return np.random.randint(1, self.max_stones + 1) | |
| def _is_valid_action(self, action): | |
| """Determine if an action is valid.""" | |
| pile, num_stones = action | |
| return 0 <= pile < self.num_piles and 0 < num_stones <= self.max_stones and num_stones <= self.piles[pile] | |
| def _is_game_over(self): | |
| """Determine if the game has ended.""" | |
| return all(pile == 0 for pile in self.piles) | |
| def _calculate_reward(self): | |
| """Calculate the reward for the current step.""" | |
| return 1 if self._is_game_over() else 0 | |