What you want is a perfect hash function, that is inexpensive in computing time?

Why not ask for something simple, like a perpetum mobile? :-)

The $seed $input is the place in the original list? Maybe permutation encryption algorithms? But to keep them below $max...?

Update: If you could keep $max to a power of 2, you could maybe XOR with a constant? (Update2: The $seed (constant) would also have to be as many bits as $max.)

Code example for Update (n.b. $max must be 2^X):

my $max  = 8;
my $list = [10, 20, 30, 40, 50, 60, 70, 80];

for(my $seed = 0; $seed < $max; $seed++) {
    print "With seed $seed: ";
    for(my $i = 0; $i < @$list; $i++) {
        my $place = get_rand($i, $seed);
        print "$place:", $list->[$place], "  ";
    }
    print "\n";
}

sub get_rand {
    my($item, $seed) = @_;

    return $item ^ $seed;
}


__END__

# -------------------------------------------
# output:
With seed 0: 0:10  1:20  2:30  3:40  4:50  5:60  6:70  7:80
With seed 1: 1:20  0:10  3:40  2:30  5:60  4:50  7:80  6:70
With seed 2: 2:30  3:40  0:10  1:20  6:70  7:80  4:50  5:60
With seed 3: 3:40  2:30  1:20  0:10  7:80  6:70  5:60  4:50
With seed 4: 4:50  5:60  6:70  7:80  0:10  1:20  2:30  3:40
With seed 5: 5:60  4:50  7:80  6:70  1:20  0:10  3:40  2:30
With seed 6: 6:70  7:80  4:50  5:60  2:30  3:40  0:10  1:20
With seed 7: 7:80  6:70  5:60  4:50  3:40  2:30  1:20  0:10

[download]

In reply to Re: Random 1-1 mapping by BerntB
in thread Random 1-1 mapping by tomazos

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.