perl -e '
for $n(10..14) {
  $str = "x"x($n*2+1); 
  $t=time;
  $str =~ /(x+x+){$n}y/;
  print "\$str:$str n:$n time:",time-$t,"sec\n"
}'
$str:xxxxxxxxxxxxxxxxxxxxx n:10 time:0sec
$str:xxxxxxxxxxxxxxxxxxxxxxx n:11 time:3sec
$str:xxxxxxxxxxxxxxxxxxxxxxxxx n:12 time:9sec
$str:xxxxxxxxxxxxxxxxxxxxxxxxxxx n:13 time:39sec
$str:xxxxxxxxxxxxxxxxxxxxxxxxxxxxx n:14 time:156sec

##</code><code>##

perl -e '
for $n(1..14) {
  $str = "x"x($n*3+1); 
  $t=time;
  $str =~ /(x+x+x+){$n}y/;
  print "\$str:$str n:$n time:",time-$t,"sec\n"
}'
$str:xxxx n:1 time:0sec
$str:xxxxxxx n:2 time:0sec
$str:xxxxxxxxxx n:3 time:0sec
$str:xxxxxxxxxxxxx n:4 time:0sec
$str:xxxxxxxxxxxxxxxx n:5 time:0sec
$str:xxxxxxxxxxxxxxxxxxx n:6 time:0sec
$str:xxxxxxxxxxxxxxxxxxxxxx n:7 time:1sec
$str:xxxxxxxxxxxxxxxxxxxxxxxxx n:8 time:9sec
$str:xxxxxxxxxxxxxxxxxxxxxxxxxxxx n:9 time:73sec
$str:xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx n:10 time:555sec
^C