#!/usr/bin/env perl
use strict;
use warnings;
use feature 'say';

my @queue = '123456789';

my %seen;

while (@queue) {
    local $_ = shift @queue;
    next if (exists $seen{$_});
    $seen{$_}++;
    say if eval == 100;
    while (/\d+?/g) {
        my ($pre,$match,$post) = ($`,$&,$');
        push @queue, "$pre$match+$post" unless (!$post || $post =~ /[+-]/);
        push @queue, "$pre-$match$post" unless ($pre =~ /[-+]$/ );
    }
}