Re: A little arithmetic puzzle

[Rob Williams]

Brute force, but still fairly fast.

#!/usr/bin/perl
use strict;
my @symbols = qw(+ - / *);
my %done;
while (1) {
       my $equ;
       $equ .= "$_".$symbols[int(rand(4))] for (sort { (-1,1)[rand 2] } 
qw(1 5 6 7));
       chop($equ);
       while (!$done{$equ}++){
               &ev($equ, @$_) for 
([0,4],[0,0,5,8],[0,0,6,5,13,14],[2,6],[2,8],[2,14]);   #could add more 
I guess.
       }
}
sub ev {
       my ($exp, @arr) = @_;
       my @exp = split '', $exp;
       my $cnt = 0;
       for (@arr) {
               my $br = (++$cnt <= (scalar(@arr) / 2)) ? '(' : ')';
               splice(@exp,$_,0,$br);
       }
       $exp = join '', @exp;
       (print "$exp\n" and exit) if eval(join '', $exp) == 21;
}