%{
#include <stdio.h>
 
// State definitions
#define S0 0  // Even a, Even b (start)
#define S1 1  // Odd a, Even b (accepting)
#define S2 2  // Even a, Odd b
#define S3 3  // Odd a, Odd b
 
int state = S0;
%}
 
%%
a  {
    if (state == S0) state = S1;
    else if (state == S1) state = S0;
    else if (state == S2) state = S3;
    else if (state == S3) state = S2;
}
b  {
    if (state == S0) state = S2;
    else if (state == S1) state = S3;
    else if (state == S2) state = S0;
    else if (state == S3) state = S1;
}
\n {
    if (state == S1)
        printf("Accepted\n");
    else
        printf("Rejected\n");
 
    state = S0; // Reset for next string
}
.  ; // Ignore other characters
%%
 
int main() {
    printf("Enter strings (press Ctrl+D to stop):\n");
    yylex();
    return 0;
}
 

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