If you're gonna get this nuts about speed, you may as well fire up Inline C or XS. If you know XS, this solution is actually easier to grok than some of the more esoteric solutions above, as well as faster:

!/usr/bin/perl
use strict;
use warnings;

# fast_uniq.plx -- 10 unique digits in a 10-char string

use Benchmark qw( cmpthese );
use Inline C => <<'END_C';

/* works for ASCII, EBCDIC, UTF-8 */

int offset;
SV* digits_sv;

void prime_variables (SV* input_sv, SV* zero_sv) {
    digits_sv = newSVsv(input_sv);
    char* zero_str = SvPV_nolen(zero_sv);
    offset = *zero_str;
}

int test_uniq_digits () {
    STRLEN digits_len = SvCUR( digits_sv );
    char* string      = SvPV( digits_sv, digits_len );

    char test_buf[10] = { 0,0,0,0,0, 0,0,0,0,0 };

    int i, index;
    for (i = 0; i < 10; i++) {
        index = *string - offset;
        if (index < 0 || index > 9) 
            croak("illegal character: '%c'", *string);
        if (test_buf[index] == 1)
            return 0;
        test_buf[index] = 1;
        string++;
    }   
    return 1;
}

END_C

run_test("0123456789", "UNIQUE:\n");
run_test("1123456789", "NOT_UNIQUE:\n");

sub run_test {
    my ($digits, $message) = @_;
    prime_variables($digits, "0");
    print $message;
    cmpthese( -5, {
        u1 => sub {
                   for ( 0 .. 9 ) { 
                      return 0 if $digits !~ /$_/;
                   }       
                   return 1;
                 },      
        u1000 => sub { test_uniq_digits },
    });
    print "\n\n";
}
[download]

Here's the output:

UNIQUE:
          Rate    u1 u1000
u1     10619/s    --  -98%
u1000 692527/s 6421%    --


NOT_UNIQUE:
          Rate    u1 u1000
u1    414417/s    --  -42%
u1000 712019/s   72%    --
[download]

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