#!/usr/local/bin/perl

use 5.010;

use strict;
use warnings FATAL => 'all';

my $hex = '7c9695cb23a71d851688cc0d7f8b1072';
my @num = map {hex} split '', $hex;

forty_two(42 => @num);

sub forty_two {
    my ($target, $expr, $first, @rest) = @_;
    state $count_hit   = 0;
    state $count_total = 0;

    unless (defined $first) {
        $count_total++;
        if (eval $expr == $target) {
            $count_hit++;
            $expr =~ s/(\d+)/sprintf "%x", $1/eg;
            say "$count_hit/$count_total: $expr == 42";
        }
        return;
    }

    forty_two($target, "$expr+$first", @rest);
    forty_two($target, "$expr-$first", @rest);
    forty_two($target, "$expr*$first", @rest);
    if ($first) {
        my ($last_term) = $expr =~ m{(\d+(?:[*/]\d+)*)$};
        forty_two($target, "$expr/$first", @rest)
          if eval "$last_term % $first == 0";
    }
}