请给我使用 PyTorch 实现 DQN 算法来玩 Pong 游戏的完整代码

好的，这是一个使用 PyTorch 实现 DQN 算法来玩 Pong 游戏的完整代码，你可以参考它：

import gym
import torch
import torch.nn as nn
import torch.optim as optim
import torch.nn.functional as F
import random
import numpy as np
from collections import deque

# 设置超参数
BATCH_SIZE = 32
GAMMA = 0.99
EPS_START = 1
EPS_END = 0.02
EPS_DECAY = 1000000
TARGET_UPDATE = 1000
MEMORY_CAPACITY = 100000
LR = 1e-4
ENV_NAME = "Pong-v0"

# 设置环境
env = gym.make(ENV_NAME)
n_actions = env.action_space.n

# 设置设备
device = torch.device("cuda" if torch.cuda.is_available() else "cpu")

# 定义神经网络
class DQN(nn.Module):
    def __init__(self):
        super(DQN, self).__init__()
        self.conv1 = nn.Conv2d(4, 32, kernel_size=8, stride=4)
        self.conv2 = nn.Conv2d(32, 64, kernel_size=4, stride=2)
        self.conv3 = nn.Conv2d(64, 64, kernel_size=3, stride=1)
        self.fc1 = nn.Linear(7 * 7 * 64, 512)
        self.fc2 = nn.Linear(512, n_actions)

    def forward(self, x):
        x = F.relu(self.conv1(x))
        x = F.relu(self.conv2(x))
        x = F.relu(self.conv3(x))
        x = x.view(x.size(0), -1)
        x = F.relu(self.fc1(x))
        x = self.fc2(x)
        return x

# 定义经验回放类
class ReplayMemory(object):
    def __init__(self, capacity):
        self.capacity = capacity
        self.memory = deque(maxlen=capacity)

    def push(self, state, action, reward, next_state, done):
        self.memory.append((state, action, reward, next_state, done))

    def sample(self, batch_size):
        batch = random.sample(self.memory, batch_size)
        state, action, reward, next_state, done = zip(*batch)
        return state, action, reward, next_state, done

    def __len__(self):
        return len(self.memory)

# 定义 DQN 算法类
class DQNAgent(object):
    def __init__(self):
        self.policy_net = DQN().to(device)
        self.target_net = DQN().to(device)
        self.target_net.load_state_dict(self.policy_net.state_dict())
        self.target_net.eval()

        self.optimizer = optim.Adam(self.policy_net.parameters(), lr=LR)
        self.memory = ReplayMemory(MEMORY_CAPACITY)

        self.steps_done = 0
        self.episode_durations = []
        self.episode_rewards = []

    def select_action(self, state):
        sample = random.random()
        eps_threshold = EPS_END + (EPS_START - EPS_END) * \
            np.exp(-1. * self.steps_done / EPS_DECAY)
        self.steps_done += 1
        if sample > eps_threshold:
            with torch.no_grad():
                state = torch.FloatTensor(state).unsqueeze(0).to(device)
                q_value = self.policy_net(state)
                action = q_value.max(1)[1].view(1, 1)
        else:
            action = torch.tensor([[random.randrange(n_actions)]], device=device, dtype=torch.long)
        return action

    def optimize_model(self):
        if len(self.memory) < BATCH_SIZE:
            return
        state, action, reward, next_state, done = self.memory.sample(BATCH_SIZE)

        state_batch = torch.FloatTensor(state).to(device)
        action_batch = torch.LongTensor(action).unsqueeze(1).to(device)
        reward_batch = torch.FloatTensor(reward).to(device)
        next_state_batch = torch.FloatTensor(next_state).to(device)
        done_batch = torch.FloatTensor(done).to(device)

        q_values = self.policy_net(state_batch).gather(1, action_batch)

        next_q_values = torch.zeros(BATCH_SIZE, device=device)
        next_q_values[~done_batch] = self.target_net(next_state_batch[~done_batch]).max(1)[0].detach()

        expected_q_values = (next_q_values * GAMMA) + reward_batch

        loss = F.smooth_l1_loss(q_values, expected_q_values.unsqueeze(1))

        self.optimizer.zero_grad()
        loss.backward()
        self.optimizer.step()

    def train(self, num_episodes):
        for i_episode in range(num_episodes):
            state = env.reset()
            state = np.stack((state, state, state, state), axis=0)
            episode_reward = 0
            for t in range(10000):
                action = agent.select_action(state)
                next_state, reward, done, _ = env.step(action.item())
                episode_reward += reward
                next_state = np.append(np.expand_dims(next_state, 0), state[:3, :, :], axis=0)
                agent.memory.push(state, action.item(), reward, next_state, done)
                state = next_state

                agent.optimize_model()
                if done:
                    agent.episode_durations.append(t + 1)
                    agent.episode_rewards.append(episode_reward)
                    if i_episode % 10 == 0:
                        print("Episode: {}, Reward: {}".format(i_episode, episode_reward))
                    break

            if i_episode % TARGET_UPDATE == 0:
                agent.target_net.load_state_dict(agent.policy_net.state_dict())

        env.close()

if __name__ == "__main__":
    agent = DQNAgent()
    agent.train(1000)

注意：这段代码需要安装 gym 和 PyTorch 库。在运行代码之前，请确保你已经按照这些库。