#!/usr/bin/perl -w

use strict;

sub sum {
    my $sum = 0;
    $sum += $_ for @_;
    return $sum;
}

for (1..10) {
    my $copy = my $number = int rand 1e4;

    print "=== Test: $_ - Number: $number ===\n";

    print "Brute force:\n";
    while ($copy > 9) {
        my @digits = split //, $copy;
        $copy = sum(@digits);
        print "\t", join(' + ', @digits), " = $copy\n";
    }

    print "Maths:\n";
    print "\t$number % 9 || 9 = ", $number % 9 || 9, "\n\n";
}