project-euler/Perl/068 Magic 5-gon ring.pl

#!/usr/bin/perl

# Author: Daniel "Trizen" Șuteu
# License: GPLv3
# Website: https://github.com/trizen

# https://projecteuler.net/problem=68

# Runtime: 4.326s

use strict;
use integer;
use ntheory qw(forperm);

my $max  = '';
my @nums = (1 .. 10);

forperm {
    my @d = @nums[@_];

    my $i = $d[0] + $d[1] + $d[2];
    my $j = $d[3] + $d[2] + $d[4];
    my $k = $d[5] + $d[4] + $d[6];
    my $l = $d[7] + $d[6] + $d[8];
    my $m = $d[9] + $d[8] + $d[1];

    if (    $d[0] < $d[3]
        and $d[0] < $d[5]
        and $d[0] < $d[7]
        and $d[0] < $d[9]
        and $i == $j
        and $i == $k
        and $i == $l
        and $i == $m
    ) {
        my $str = "$d[0]$d[1]$d[2]$d[3]$d[2]$d[4]$d[5]$d[4]$d[6]$d[7]$d[6]$d[8]$d[9]$d[8]$d[1]";
        if (length($str) == 16 and $max lt $str) {
            $max = $str;
        }
    }
} scalar(@nums);

print "$max\n";