「7の倍数」を表す正規表現

x7.pl

#!/usr/bin/perl

# https://qiita.com/jkr_2255/items/8bae27d026754d4e2474
# 「7の倍数」を表す正規表現

use v5.24;
use warnings;
use Data::Dumper;

my $NUM_STATES = 7;
my @states;

my @BASE = qw( [07] [18] [29] 3 4 5 6 );

for my $from (0..6) {
  for my $to (0..6) {
    $states[$from][$to] = sprintf("%s", $BASE[($to - 10 * $from) % 7]);
  }
}

for my $n (reverse(1 .. $NUM_STATES - 1)) {
  for my $i (0..$n) {
    for my $j (0..$n) {
      $states[$i][$j] = sprintf("(%s|%s)",
        $states[$i][$j],
        qq/$states[$i][$n]$states[$n][$n]*$states[$n][$j]/
      )
    }
  }
}

my $re = qr/\A$states[0][0]+\z/n;
say $re;

my $count = 200;
my $match;
for (1 .. $count) {
    my $rand = int rand(~0 >> 1);
    my $mod = $rand % 7;
    if ($rand =~ /$re/) {
	$match++;
	if ($mod) {
	    say "$rand\tmod=$mod"
	} else {
	    printf "$rand = %d * 7 + %d\n", $rand / 7, $mod;
	}
    } else {
	say "$rand\terror" if $mod == 0;
    }
}
printf "%d/%d = %f\n", $match, $count, $match / $count;