mergesort

#!/usr/bin/env perl

use 5.014;
use warnings;
use strict;
use autodie;

my @unsorted = map { int(rand(100)) } 1..20;
say join ' ', @unsorted;

sub mergesort {
    my @items = @_;
    if (@items <= 1) { @items }
    else { merge([mergesort(splice @items, 0, ($#items+1)/2)],[mergesort(@items)]) }
}

sub merge {
    my @l1 = @{shift @_};
    my @l2 = @{shift @_};
    if (!@l2) { @l1 }
    elsif (!@l1) { @l2 }
    else {
        my ($a,$b) = (shift @l1,shift @l2);
        $a < $b ? ($a,merge([@l1],[$b,@l2])) : ($b,merge([$a,@l1],[@l2]));
    }
}

my @sorted = mergesort(@unsorted);
say join ' ', @sorted;