请把功能实现里的代码写出来

好的，下面是部分功能实现的代码：

1. 贪吃蛇的移动和转向：

public class Snake : MonoBehaviour {
    public float speed = 1.0f; // 贪吃蛇移动速度
    private Vector3 direction = Vector3.right; // 贪吃蛇移动方向

    void Update () {
        if (Input.GetKey(KeyCode.UpArrow))
            direction = Vector3.up;
        else if (Input.GetKey(KeyCode.DownArrow))
            direction = Vector3.down;
        else if (Input.GetKey(KeyCode.LeftArrow))
            direction = Vector3.left;
        else if (Input.GetKey(KeyCode.RightArrow))
            direction = Vector3.right;
    }

    void FixedUpdate() {
        transform.position += direction * speed * Time.deltaTime;
    }
}

2. 食物的生成和消失：

public class FoodSpawner : MonoBehaviour {
    public GameObject foodPrefab; // 食物预制体
    public float spawnInterval = 5.0f; // 食物生成间隔时间

    void Start () {
        InvokeRepeating("SpawnFood", spawnInterval, spawnInterval);
    }

    void SpawnFood () {
        float x = Random.Range(-9, 9);
        float y = Random.Range(-4, 4);
        Instantiate(foodPrefab, new Vector3(x, y, 0), Quaternion.identity);
    }
}

public class Food : MonoBehaviour {
    void OnTriggerEnter2D(Collider2D other) {
        if (other.CompareTag("Player")) {
            Destroy(gameObject);
            ScoreManager.instance.IncreaseScore();
        }
    }
}

public class ScoreManager : MonoBehaviour {
    public static ScoreManager instance;
    private int score = 0;

    void Awake() {
        if (instance == null)
            instance = this;
        else if (instance != this)
            Destroy(gameObject);
    }

    public void IncreaseScore() {
        score++;
        Debug.Log("Score: " + score);
    }
}

3. 得分计算：

public class ScoreManager : MonoBehaviour {
    public static ScoreManager instance;
    private int score = 0;

    void Awake() {
        if (instance == null)
            instance = this;
        else if (instance != this)
            Destroy(gameObject);
    }

    public void IncreaseScore() {
        score++;
        Debug.Log("Score: " + score);
    }
}

4. 碰撞检测：

public class Snake : MonoBehaviour {
    void OnTriggerEnter2D(Collider2D other) {
        if (other.CompareTag("Boundary") || other.CompareTag("Snake")) {
            // 游戏结束
        }
    }
}

5. 游戏结束判断：

public class Snake : MonoBehaviour {
    void OnTriggerEnter2D(Collider2D other) {
        if (other.CompareTag("Boundary") || other.CompareTag("Snake")) {
            GameOver();
        }
    }

    void GameOver() {
        // 显示游戏结束界面
    }
}

6. 难度设置：

public class GameManager : MonoBehaviour {
    public float speed = 1.0f; // 贪吃蛇移动速度
    public float spawnInterval = 5.0f; // 食物生成间隔时间

    void Start () {
        // 根据难度设置调整游戏参数
    }
}

7. 游戏界面交互：

public class UIManager : MonoBehaviour {
    public void StartGame() {
        // 开始游戏
    }

    public void RestartGame() {
        // 重新开始游戏
    }

    public void QuitGame() {
        // 退出游戏
    }
}

8. 音效添加：

public class SoundManager : MonoBehaviour {
    public AudioSource bgm; // 游戏音乐
    public AudioSource moveSound; // 贪吃蛇移动音效
    public AudioSource eatSound; // 食物吃掉音效

    public void PlayBGM() {
        bgm.Play();
    }

    public void PlayMoveSound() {
        moveSound.Play();
    }

    public void PlayEatSound() {
        eatSound.Play();
    }
}

以上是部分功能实现的代码，具体实现方式可能有所不同，仅供参考。