use strict;
use Benchmark::Timer; my $T = new Benchmark::Timer;

no warnings 'recursion';

my($Ack,$Fib,$Tak);
$Ack = sub
{
        my ($x, $y) = @_;

        return $y + 1         if $x == 0;
        return $Ack->($x - 1, 1) if $y == 0;

        $Ack->($x - 1, $Ack->($x, $y - 1));
};

sub Ack {
    my( $x, $y ) = @_;
    my @stack;

    push @stack, $x;
    do {
        $x = pop @stack;
        if( $x == 0 ) {
            ++$y;
        }
        elsif( $y == 0 ) {
            push @stack, $x - 1;
            $y = 1;
        }
        else {
            push @stack, $x - 1, $x;
            --$y;
        }
    } while @stack;
    return $y;
}


my $n = ($ARGV[0] || 0) - 1;
$T->start( 'Recursive Ack 3,' . ( $n+1 ) );
printf "Ack(%d,%d): %d\n",
        3, $n + 1, $Ack->(3, $n + 1);
$T->stop( 'Recursive Ack 3,' . ( $n+1 ) );

$T->start( 'Iterative Ack 3,' . ( $n+1 ) );
printf "Ack(%d,%d): %d\n",
        3, $n + 1, Ack( 3, $n + 1 );
$T->stop( 'Iterative Ack 3,' . ( $n+1 ) );
$T->report;