>perl -wMstrict -le
"for my $s (qw(
   AAA RR XXK AxA xAxxYxxRx
   A xAx ARKYGZX XxZxGxYxKxRxA AxAxAxA xYYYYx xRRRRRx RRRR
   )) {
   my $n = $s =~ tr{ARKYGZX}{};
   printf qq{%s match : '%s' \n},
         ($n == 2 || $n == 3) ? '  ' : 'NO', $s;
   }
"
   match : 'AAA'
   match : 'RR'
   match : 'XXK'
   match : 'AxA'
   match : 'xAxxYxxRx'
NO match : 'A'
NO match : 'xAx'
NO match : 'ARKYGZX'
NO match : 'XxZxGxYxKxRxA'
NO match : 'AxAxAxA'
NO match : 'xYYYYx'
NO match : 'xRRRRRx'
NO match : 'RRRR'