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Designing Non-Deterministic Finite Automata (Set 4)

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  • Difficulty Level : Hard
  • Last Updated : 02 Nov, 2022
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Prerequisite: Finite Automata Introduction In this article, we will see some designing of Non-Deterministic Finite Automata (NFA). Problem-1: Construction of a minimal NFA accepting a set of strings over {a, b} in which each string of the language contain ‘a’ as the substring. Explanation: The desired language will be like:

L1 = {ab, abba, abaa, ...........}

Here as we can see that each string of the above language contains ‘a’ as the substring. But the below language is not accepted by this NFA because some of the string of below language does not contain ‘a’ as the substring.

L2 = {bb, b, bbbb, .............}

The state transition diagram of the desired language will be like below: In the above NFA, the initial state ‘X’ on getting ‘a’ as the input it transits to a final state ‘Y’ and on getting ‘b’ as the input it remains in the state of itself. The final state ‘Y’ on getting either ‘a’ or ‘b’ as the input it remains in the state of itself. Refer for DFA of above NFA.

Transition Table :

In this table initial state is depicted by —> and final state is depicted by *.

STATES INPUT (a) INPUT (b)
—> X Y* X
Y* Y* Y*

Python implementation:

Python3




def stateX(n):
    #if length of n become 0
    #then print not accepted
    if(len(n)==0):
        print("string not accepted")
         
    else:
        #if at zero index
        #'a' found then call
        #stateY function
        if (n[0]=='a'):
            stateY(n[1:])
         
        #if at zero index
        #'b' then call
        #stateX function
        elif (n[0]=='b'):
            stateX(n[1:])
        
def stateY(n):
    #if length of n become 0
    #then print accepted
    if(len(n)==0):
        print("string accepted")
         
    else
        #if at zero index
        #'a' found call
        #stateY function  
        if (n[0]=='a'):
            stateY(n[1:])
             
        #if at zero index
        #'b' found call
        #stateY function
        elif (n[0]=='b'):
            stateY(n[1:])
             
 
#take input
n=input()
 
#call stateA function
#to check the input
stateX(n)


Problem-2: Construction of a minimal NFA accepting a set of strings over {a, b} in which each string of the language is not containing ‘a’ as the substring. Explanation: The desired language will be like:

L1 = {b, bb, bbbb, ...........}

Here as we can see that each string of the above language is not containing ‘a’ as the substring But the below language is not accepted by this NFA because some of the string of below language is containing ‘a’ as the substring.

L2 = {ab, aba, ababaab..............}

The state transition diagram of the desired language will be like below: In the above NFA, the initial and final state ‘Y’ on getting ‘b’ as the input it remains in the state of itself.

Transition Table :

In this table initial state is depicted by —> and final state is depicted by *.

STATES INPUT (a) INPUT (b)
—> Y * Y* Y*

Python Implementation:

Python3




def stateY(n):
    #if length of n become 0
    #then print accepted
    if(len(n)==0):
        print("string accepted")
         
    else
        #if at zero index
        #'a' found then
        #print not accepted  
        if (n[0]=='a'):
            print("String not accepted")
             
        #if at zero index
        #'b' found call
        #stateY function
        elif (n[0]=='b'):
            stateY(n[1:])
             
 
#take input
n=input()
 
#call stateY function
#to check the input
stateY(n)



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