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#! /usr/bin/env perl
#
use 5.22.0;
use warnings;
use feature 'signatures';
no warnings 'experimental::signatures';
use integer;
# really need the big integers when $m >= 4
# use bigint lib => 'GMP';
no warnings 'recursion';
my $count = 0;
sub _ack( $m, $n ) {
state @known;
$count++;
return $known[$m][$n] ||= do {
!$m ? $n + 1 :
!$n ? _ack($m - 1, 1) :
_ack($m - 1, _ack($m, $n - 1));
};
}
sub ack ( $m, $n ) {
die "the function is not defined for negative parameters" if $m < 0 || $n < 0;
return _ack($m, $n);
}
die "must give two nonnegative integers as input" unless @ARGV > 1;
$" = ', ';
say "A( @ARGV ) = ", ack(@ARGV), " ...after $count calls.";
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