#!/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 (reverse 1..3); #@A is empty now.

print join( ' ',@$_)," : ",scalar @$_,$/ for @parts;