Aim: Write a program to check wether a string belongs to the grammer or not.
#include <iostream>
using namespace std;
bool checkGrammar1(string str) {
if (str[0] != 'a' || str[str.length() - 1] != 'b') {
return false;
}
for (int i = 1; i < str.length(); i++) {
if (str[i - 1] == 'b' && str[i] == 'a') {
return false;
}
}
return true;
}
bool checkGrammar2(string str) {
int n = str.length();
if (n % 2 == 0) {
return false;
}
for (int i = 0; i < n / 2; i++) {
if ((str[i] != 'a' && str[i] != 'b') || (str[n - 1 - i] != 'a' && str[n - 1 - i] != 'b')) {
return false;
}
if (str[i] != str[n - 1 - i]) {
return false;
}
}
return true;
}
bool checkGrammar3(string str) {
int n = str.length();
int cntA = 1, cntB = 0;
if (n == 0) {
return false;
}
if (str[0] != 'a' || str[n - 1] != 'b') {
return false;
}
for (int i = 1; i < str.length(); i++) {
if (str[i] == 'a') {
cntA++;
} else if (str[i] == 'b') {
cntB++;
} else {
return false;
}
if (str[i - 1] == 'b' && str[i] == 'a') {
return false;
}
}
if (cntA * 2 != cntB) {
return false;
}
return true;
}
string p(bool flag) {
if (flag) {
return "true";
} else {
return "false";
}
}
int main() {
cout << "1. Grammar 1 2. Grammar 2" << endl;
cout << "3. Grammar 3 4. End" << endl;
string s;
int n;
cout << "Enter Choice: ";
cin >> n;
while (n != 4) {
cout << "Enter String: ";
cin >> s;
if (n == 1) cout << "Checking for grammar 1: " << p(checkGrammar1(s)) << endl;
if (n == 2) cout << "Checking for grammar 2: " << p(checkGrammar2(s)) << endl;
if (n == 3) cout << "Checking for grammar 3: " << p(checkGrammar3(s)) << endl;
cout << "Enter Choice: ";
cin >> n;
}
return 0;
}
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