Heapsort

#!/usr/bin/perl

use warnings;
use strict;

my $N = 10000000;
my @a;

sub pushDown {
    my ($pos, $N) = @_;
    while (2 * $pos + 1 < $N) {
        my $j = 2 * $pos + 1;
        if ($j + 1 < $N && $a[$j + 1] > $a[$j]) {
            ++$j;
        }
        last if $a[$pos] >= $a[$j];
        @a[$pos, $j] = @a[$j, $pos];
        $pos = $j;
    }
}

@a = 0 .. $N-1;

pushDown($_, $N) for reverse 0 .. $N / 2;

my $n = $N;
while ($n > 1) {
    @a[0, $n - 1] = @a[$n - 1, 0];
    --$n;
    pushDown(0, $n);
}

while (my ($id, $key) = each @a) {
    die unless $id == $key;
}