The Algorithms
Pushdown Automata Implementation
D
A Simple Implementation of Push Down Automaton:
Defining the 6 tuples:
- Q-->finite set of sets
- Sigma-->finite set of input alphabet
- Gamma-->finite set of stack alphabet
- Delta-->transition relation
- Q0-->start state
- Z-->initial stack symbol
- F-->set of accepting states
Defining the states:
state 0: starting state
state 1:From state 0 whenever it sees a 1 or 2, it moves to state 1+pushes the element onto the stack
state 1:From state 1 whenever it sees a 1 or 2, it remains in state 1+pushes the element onto the stack
state 2:From state 1 whenever it sees a 0, it moves to state 2+pops from the stack
state 2:From state 1 whenever it sees a 0, it remains in state 2+pops from the stack
state 3:From state 0, if it sees a 0,it moves to state 3,the rejected state
state 3:From state 2, if it sees a 1 or 2 , it moves to state 3, the rejected state
state 3:If at the end, the stack is not empty, it moves to state 3,the rejected state
#stack functions
def push(a,list1):
#pushing to the stack/adding to the top of the stack
list1.append(a)
return 1
def pop(list1):
#for poping from the stack/removing the top element of the stack
index=len(list1)-1
if (index>0):
list1.pop(index)
return 1
else:
return 0
# Q={0,1,2,3}
# Sigma={0,1,2}
# Starting state={0}
# Z=#
# F={2}
#setting the initial stack symbol
stack=['#']
#setting the starting state
state=0
#taking the input
input_string=input('Enter the String:')
#performing the operations
l=len(input_string)
i=0
if l%2==0:
while i<l//2:
letter=int(input_string[i])
#print(letter)
if letter in [1,2]:
push(letter,stack)
state=1
#print(">state=1")
else :
state=3
#print(">1.state=3")
break
i+=1
while i<l:
letter=int(input_string[i])
#print(letter)
if state==3:
break
if letter==0:
state=2
#print(">2.state=2")
pop(stack)
else:
state=3
#print(">2.state=3")
break
i+=1
else:
state=3
#print("3state=3")
if state==2 and len(stack)!=1:
state=3
#print(state)
#print(len(stack))
#checking the final state and displaying the result
if(state==2):
print("The String is accepted")
else:
print("The String is rejected")Enter the String:123456
The String is rejected
