Another one...

#!/usr/bin/perl -w

use strict;

my @A= 1..int(rand(21));
print "\@A: ",scalar @A,$/;

my @parts;
$parts[3-$_] = [splice @A,0, @A%$_?int(@A/$_)+1:int(@A/$_)] foreach (r
+everse 1..3); #@A is empty now.

print join( ' ',@$_)," : ",scalar @$_,$/ for @parts;
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But I prefer the one posted by TedPride.