24 game/Solve

A loose translation of the Perl entry. Does not return every possible permutation of the possible solutions. Filters out duplicates (from repeated digits) and only reports the solution for a particular order of digits and operators with the fewest parenthesis (avoids reporting duplicate solutions only differing by unnecessary parenthesis). Does not guarantee the order in which results are returned.

Since Perl 6 uses Rational numbers for division (whenever possible) there is no loss of precision as is common with floating point division. So a comparison like (1 + 7) / (1 / 3) == 24 "Just Works"^™

use MONKEY-SEE-NO-EVAL;

my @digits;
my $amount = 4;

# Get $amount digits from the user,
# ask for more if they don't supply enough
while @digits.elems < $amount {
    @digits.append: (prompt "Enter {$amount - @digits} digits from 1 to 9, "
    ~ '(repeats allowed): ').comb(/<[1..9]>/);
}
# Throw away any extras
@digits = @digits[^$amount];

# Generate combinations of operators
my @ops = [X,] <+ - * /> xx 3;

# Enough sprintf formats to cover most precedence orderings
my @formats = (
    '%d %s %d %s %d %s %d',
    '(%d %s %d) %s %d %s %d',
    '(%d %s %d %s %d) %s %d',
    '((%d %s %d) %s %d) %s %d',
    '(%d %s %d) %s (%d %s %d)',
    '%d %s (%d %s %d %s %d)',
    '%d %s (%d %s (%d %s %d))',
);

# Brute force test the different permutations
for unique @digits.permutations -> @p {
    for @ops -> @o {
        for @formats -> $format {
            my $string = sprintf $format, flat roundrobin(|@p; |@o);
            my $result = EVAL($string);
            say "$string = 24" and last if $result and $result == 24;
        }
    }
}

# Only return unique sub-arrays
sub unique (@array) {
    my %h = map { $_.Str => $_ }, @array;
    %h.values;
}

Output:

Enter 4 digits from 1 to 9, (repeats allowed): 3711
(1 + 7) * 3 * 1 = 24
(1 + 7) * 3 / 1 = 24
(1 * 3) * (1 + 7) = 24
3 * (1 + 1 * 7) = 24
(3 * 1) * (1 + 7) = 24
3 * (1 / 1 + 7) = 24
(3 / 1) * (1 + 7) = 24
3 / (1 / (1 + 7)) = 24
(1 + 7) * 1 * 3 = 24
(1 + 7) / 1 * 3 = 24
(1 + 7) / (1 / 3) = 24
(1 * 7 + 1) * 3 = 24
(7 + 1) * 3 * 1 = 24
(7 + 1) * 3 / 1 = 24
(7 - 1) * (3 + 1) = 24
(1 + 1 * 7) * 3 = 24
(1 * 1 + 7) * 3 = 24
(1 / 1 + 7) * 3 = 24
(3 + 1) * (7 - 1) = 24
3 * (1 + 7 * 1) = 24
3 * (1 + 7 / 1) = 24
(3 * 1) * (7 + 1) = 24
(3 / 1) * (7 + 1) = 24
3 / (1 / (7 + 1)) = 24
(1 + 3) * (7 - 1) = 24
(1 * 3) * (7 + 1) = 24
(7 + 1) * 1 * 3 = 24
(7 + 1) / 1 * 3 = 24
(7 + 1) / (1 / 3) = 24
(7 - 1) * (1 + 3) = 24
(7 * 1 + 1) * 3 = 24
(7 / 1 + 1) * 3 = 24
3 * (7 + 1 * 1) = 24
3 * (7 + 1 / 1) = 24
3 * (7 * 1 + 1) = 24
3 * (7 / 1 + 1) = 24

Enter 4 digits from 1 to 9, (repeats allowed):  5 5 5 5
5 * 5 - 5 / 5 = 24

Enter 4 digits from 1 to 9, (repeats allowed): 8833
8 / (3 - 8 / 3) = 24