View difference between Paste ID: nBSKRPzy and huRLy5mT

 #!/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;
 }