How to find an unreachable state in C? Observe text file below. It is a state ma

Question

How to find an unreachable state in C? Observe text file below. It is a state machine. First column of each row is current state and second column is next state if input is 0. If input is 1 go to column 3. So if youre at C and enter 0 you go to A.

A B C

B A A

C A D

D D C

Now my program lets you change the second and third column and so you can end up in a situation where you have an unreachable state like below

A B C

B A A

C A B

D D C

So if youre not in D state you can never reach it. Now i need to write code so that on a certain command it will identify all unreachable states. Can you help me please?

Explanation / Answer

//here I have considered input in the form of 3x4 matrix,but you can change it to the number of row manually,

#include<iostream>

#include<bits/stdc++.h>

using namespace std;

int main(){

vector< vector<char> > states;

for(int i=0;i<4;i++)

{

vector<char> row;

for(int j=0;j<3;j++)

{

char a;

cin>>a;

row.push_back(a);

}

states.push_back(row);

}

set<char> reached_states;

set<char> all_states;

set<char> unreachable;

for(int i=0;i<states.size();i++)

{

for(int j=1;j<states[0].size();j++){

if(states[i][0]!=states[i][j])

{

reached_states.insert(states[i][j]);

}

all_states.insert(states[i][0]);

all_states.insert(states[i][j]);

}

}

set <char> :: iterator itr;

cout << " The set of all states is : ";

for (itr = all_states.begin(); itr != all_states.end(); ++itr)

{

cout << ' ' << *itr;

}

cout << endl;

cout << " The set reached_states is : ";

for (itr = reached_states.begin(); itr != reached_states.end(); ++itr)

{

cout << ' ' << *itr;

}

cout << endl;

set_difference (all_states.begin(), all_states.end(), reached_states.begin(), reached_states.end(), inserter(unreachable, unreachable.end()));

cout << " The set unreachable states is : ";

for (itr = unreachable.begin(); itr != unreachable.end(); ++itr)

{

cout << ' ' << *itr;

}

cout << endl;

return 0;

}

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