>perl -wMstrict -le
"my @lines = (
   'foo A A A', 'foo bar A B A', 'foo bar baz  A  A  A'
   );
 my $n = 3;
 $n -= 1;
 for my $line (@lines) {
   print qq{'$line'}
      if $line =~ m{ \b ([[:alpha:]]) (?: \s+ \1){$n} \s* \Z }xms;
   }
"
'foo A A A'
'foo bar baz  A  A  A'