use Benchmark qw( cmpthese ) ; my $digits = 2491306578; cmpthese( -5, { u1 => sub{ for ( 0 .. 9 ) { return 0 if $digits !~ /$_/;} return 1; }, u2 => sub{ my @x = sort split //, $digits; my $x = join "", @x; $x =~ tr/0-9//s; length $x == 10 ? return 1 : return 0; }, u3 => sub { return 0 if $digits =~ /(\d).*\1/; return 1; }, u4 => sub { return $digits !~ /(.).*\1/; }, } ); __END__ #### All unique: Rate u1 u2 u3 u4 u1 15504/s -- -75% -95% -95% u2 62910/s 306% -- -78% -78% u3 289343/s 1766% 360% -- -1% u4 291910/s 1783% 364% 1% -- Not Unique: Rate u1 u2 u3 u4 u1 17396/s -- -72% -98% -98% u2 62887/s 262% -- -92% -92% u3 748300/s 4202% 1090% -- -5% u4 783739/s 4405% 1146% 5% --