难一点
时间: 2023-09-21 08:07:56 浏览: 32
好的,以下是一个稍微难一点的求解first集和follow集的例题:
对于以下文法G,求其每个非终结符的first集和follow集:
```
S -> Aa | Bb
A -> Ac | d
B -> Bf | g
C -> Aa | Bd | ε
```
答案如下:
```
First(S) = {a, b, g, d}
First(A) = {a, b, d, ε}
First(B) = {f, g, ε}
First(C) = {a, b, d, f, g, ε}
Follow(S) = {$}
Follow(A) = {a, b, g, d}
Follow(B) = {a, b, g, d}
Follow(C) = {a, b, g, d}
```
希望这个例题能够帮助你更加深入地理解如何求解first集和follow集。
相关问题
mysql实际操作题难一点
当然,我可以给你介绍一道稍微难一点的MySQL实际操作题。
题目:
假设有一个名为"students"的表,包含以下字段:
- id: 学生ID,整数类型,主键
- name: 学生姓名,字符串类型
- age: 学生年龄,整数类型
- score: 学生成绩,浮点数类型
请编写一条SQL查询语句,找出每个年龄段(10岁为一个年龄段)的学生平均成绩,并按照平均成绩从高到低进行排序。
答案:
```sql
SELECT FLOOR(age/10)*10 AS age_range, AVG(score) AS avg_score
FROM students
GROUP BY age_range
ORDER BY avg_score DESC;
```
难一点的小游戏代码Python
好的,以下是一个比较难一点的 Python 文字冒险游戏代码示例:
```python
import time
# 定义房间类
class Room:
def __init__(self, name, description, north, east, south, west, item=None):
self.name = name
self.description = description
self.north = north
self.east = east
self.south = south
self.west = west
self.item = item
# 定义物品类
class Item:
def __init__(self, name, description):
self.name = name
self.description = description
# 初始化房间和物品
outside = Room("外面", "你现在在房子外面。", None, "living_room", None, None)
living_room = Room("客厅", "你现在在客厅。", "kitchen", "dining_room", None, "outside")
kitchen = Room("厨房", "你现在在厨房。", None, None, "living_room", None, Item("刀", "一把锋利的刀"))
dining_room = Room("餐厅", "你现在在餐厅。", None, None, "bedroom", "living_room")
bedroom = Room("卧室", "你现在在卧室。", "dining_room", None, None, None, Item("钥匙", "一把金色的钥匙"))
# 定义玩家类
class Player:
def __init__(self, current_room, items=None):
self.current_room = current_room
self.items = [] if items is None else items
def move(self, direction):
next_room = getattr(self.current_room, direction)
if next_room is None:
print("你不能走那个方向。")
else:
self.current_room = next_room
print(self.current_room.description)
if self.current_room.item is not None:
self.items.append(self.current_room.item)
self.current_room.item = None
print("你发现了一个新物品:", self.items[-1].name)
def show_items(self):
if len(self.items) == 0:
print("你没有任何物品。")
else:
print("你现在持有以下物品:")
for item in self.items:
print(item.name)
# 初始化玩家
player = Player(outside)
# 游戏主循环
while True:
print("你现在在", player.current_room.name)
time.sleep(1) # 延时 1 秒,增加游戏体验
command = input("你想要做什么?")
if command == "quit":
break
elif command == "north" or command == "east" or command == "south" or command == "west":
player.move(command)
elif command == "items":
player.show_items()
else:
print("我不明白你的意思。")
```
这个小游戏是一个文字冒险游戏,玩家需要通过输入命令和选择选项来探索一个虚拟世界,完成任务和解谜。在这个游戏中,玩家可以移动到不同的房间,查看自己的物品清单,以及与环境进行交互。此外,这个游戏还有一些随机事件和谜题,可以让玩家感受到更多的挑战和乐趣。