使用python编写完整的可以将正规式((ab)|b)(a|(ba)*)a转化成NFA的代码,并将NFA以文本的形式输出,并可以使用graphviz进行查看
时间: 2024-01-22 09:18:51 浏览: 124
正规式转化成NFA
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好的,下面是代码实现:
```python
import graphviz
class State:
def __init__(self, state_id, is_final=False):
self.state_id = state_id
self.is_final = is_final
self.transitions = {}
def add_transition(self, symbol, state):
if symbol not in self.transitions:
self.transitions[symbol] = []
self.transitions[symbol].append(state)
class NFA:
def __init__(self, start_state, end_state):
self.start_state = start_state
self.end_state = end_state
def to_dot_language(self):
dot = graphviz.Digraph(comment='NFA')
dot.node(str(id(self.start_state)), shape='point')
dot.node(str(id(self.end_state)), shape='doublecircle')
dot.edge(str(id(self.start_state)), str(id(self.end_state)), label='ε')
visited = set()
stack = [self.start_state]
visited.add(self.start_state)
while stack:
state = stack.pop()
for symbol, next_states in state.transitions.items():
for next_state in next_states:
dot.node(str(id(next_state)))
dot.edge(str(id(state)), str(id(next_state)), label=symbol)
if next_state not in visited:
visited.add(next_state)
stack.append(next_state)
return dot.source
def parse_regex(regex):
stack = []
state_id = 0
for c in regex:
if c == '(':
stack.append(state_id)
state_id += 1
elif c == ')':
end_state_id = state_id
start_state_id = stack.pop()
start_state = State(start_state_id)
end_state = State(end_state_id, is_final=True)
start_state.add_transition('ε', end_state)
if len(stack) > 0:
prev_start_state_id = stack[-1]
prev_start_state = State(prev_start_state_id)
prev_start_state.add_transition('ε', start_state)
stack[-1] = start_state_id
else:
stack.append(start_state_id)
elif c == '|':
start_state_id = stack[-1]
start_state = State(start_state_id)
end_state_id = state_id
end_state = State(end_state_id, is_final=True)
start_state.add_transition('ε', end_state)
prev_start_state_id = stack[-2]
prev_start_state = State(prev_start_state_id)
prev_start_state.add_transition('ε', end_state)
stack[-2] = start_state_id
state_id += 1
elif c == '*':
state_id += 1
start_state_id = stack[-1]
end_state_id = state_id
start_state = State(start_state_id)
end_state = State(end_state_id, is_final=True)
start_state.add_transition('ε', end_state)
end_state.add_transition('ε', start_state)
if len(stack) > 1:
prev_start_state_id = stack[-2]
prev_start_state = State(prev_start_state_id)
prev_start_state.add_transition('ε', start_state)
stack[-1] = start_state_id
else:
state_id += 1
start_state_id = stack[-1]
end_state_id = state_id
start_state = State(start_state_id)
end_state = State(end_state_id, is_final=True)
start_state.add_transition(c, end_state)
stack[-1] = start_state_id
if len(stack) > 1:
prev_start_state_id = stack[-2]
prev_start_state = State(prev_start_state_id)
prev_start_state.add_transition('ε', start_state)
start_state_id = stack[0]
end_state_id = state_id + 1
start_state = State(start_state_id)
end_state = State(end_state_id, is_final=True)
start_state.add_transition('ε', stack[-1])
start_state.add_transition('ε', end_state)
return NFA(start_state, end_state)
regex = '((ab)|b)(a|(ba)*)a'
nfa = parse_regex(regex)
dot_language = nfa.to_dot_language()
print(dot_language)
```
这段代码中,我们首先定义了一个状态类`State`,每个状态都有一个唯一的ID,表示它在NFA中的位置;还有一个`is_final`属性表示这个状态是否是终止状态;以及一个`transitions`字典表示从这个状态出发,可以通过哪些字符转移到哪些状态。
接着我们定义了一个NFA类,它包含了开始状态和结束状态两个属性,以便之后生成DOT语言并可视化。
然后我们定义了一个函数`parse_regex`,用于将正则表达式解析成NFA。具体地,我们使用一个栈来存储状态ID,遍历正则表达式中的每个字符。当遇到左括号时,我们将一个新的开始状态和结束状态加入到NFA中,并将开始状态和结束状态之间加一条ε转移;当遇到右括号时,我们弹出栈中最后一个左括号对应的开始状态ID,将之前的NFA片段与新的开始状态和结束状态连接起来,并加入到栈中;当遇到竖杠时,我们弹出栈中最后两个元素,将它们连接起来,并加入到栈中;当遇到星号时,我们将最后一个元素作为开始状态,新建一个结束状态,将开始状态与结束状态之间加一条ε转移,结束状态与开始状态之间也加一条ε转移。最后,我们将左右两端的开始和结束状态连接起来。
最后,我们可以使用DOT语言生成一个图形表示NFA,并输出DOT语言字符串。可以通过安装graphviz,并运行以下命令将DOT语言渲染成PNG图片:
```python
# 安装graphviz
!pip install graphviz
# 渲染PNG图片
from graphviz import Source
s = Source.from_file('test.dot', format='png')
s.view()
```
这样就可以查看生成的NFA图像了。
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