修改了一些小错误
# -*- coding: UTF-8 -*-
"""
确定性下推自动机，Deterministic PushDown Automaton
"""
# 定义一个栈
class Stack(object):
# 初始时栈底的元素
def __init__(self, init):
self.__storage = init
def top(self):
return self.__storage[-1]
def push(self, p):
# 压入的内容做遍历，靠近后面的内容应该先被压入
for i in reversed(p):
self.__storage.append(i)
def pop(self):
return self.__storage.pop()
# 名词[配置]表示一个状态和一个栈的组合，其实上相当于以前的[一个状态]
# 为什么要定义[配置]呢？目的在于把状态和栈这两种元素组合起来形成一个整体，方便使用
class PDAConfiguration(object):
def __init__(self, state, stack):
self.state = state
self.stack = stack
# DDPA的转移规则
class PDARule(object):
# 参数：当前状态，输入，下一个状态，（栈）弹出字符，压入字符
def __init__(self, state, character, next_state, pop_character, push_characters):
self.state = state
self.character = character
self.next_state = next_state
self.pop_character = pop_character
self.push_characters = push_characters
# 下一个配置：1. 下一个状态就是 next_state 参数，2. 下一个配置的栈由方法 next_stack 根据当前的栈信息算出
def follow(self, configuration):
return PDAConfiguration(self.next_state, self.__next_stack(configuration.stack))
# 判断指定配置执行指定输入时是否可用当前的转移规则
def applies_to(self, configuration, character):
#判断会不会发生自动转移
return self.state == configuration.state \
and self.pop_character == configuration.stack.top() and self.character == character
# 下一个栈的计算，先弹出再压入即可
def __next_stack(self, stack):
stack.pop() # 弹出
stack.push(self.push_characters) # 压入
return stack
# 转移规则集合
class DPDARulebook(object):
def __init__(self, rule_set):
self.ruleSet = rule_set
# 用于获取下一个配置
def next_configuration(self, configuration, character):
return self.__rule_for(configuration, character).follow(configuration)
# 根据当前的配置和输入来查找对应的转移规则
def __rule_for(self, configuration, character):
for rule in self.ruleSet:
if rule.applies_to(configuration, character):
return rule
raise Exception("找不到可供使用的规则 ...")
rulebook = DPDARulebook([
PDARule(1, '(', 2, '$', ['b', '$']),
PDARule(2, '(', 2, 'b', ['b', 'b']),
PDARule(2, ')', 2, 'b', []),
PDARule(2, None, 1, '$', ['$'])
])
class DPDA(object):
# 参数：初始配置，接受状态，规则集合
def __init__(self, current_configuration, accept_states, rule_book):
self.current_configuration = current_configuration
self.accept_states = accept_states
self.rule_book = rule_book
# 判断当前的状态是否是接受状态
def accepting(self):
return self.current_configuration.state in self.accept_states
# 输入
def read_character(self, character):
self.current_configuration = self.rule_book.next_configuration(self.current_configuration, character)
#使状态自动转移
if (self.current_configuration.stack.top() == '$' and self.current_configuration.state == 2):
self.current_configuration.state=1
# 同样为了简化操作，方便连续输入
def read_string(self, string):
for c in string:
self.read_character(c)
if __name__ == '__main__':
dpda = DPDA(PDAConfiguration(1, Stack(['$'])), [1], rulebook)
print(dpda.accepting())
dpda.read_string('(())') #用来匹配的文本
print(dpda.accepting())
