use strict;

my @nums=split('', $number);  # the number to work on

my(@most_common, %once, %common);

my $mcc=2; # if there are no common substrings don't store

while( @nums > 4)
{
  my $key = join('', @nums[0..4]);
  $common{$key}++;
  if($common{$key} > $mcc)
  {
    $mcc=$common{$key};
    @most_common=($key); #new max set entire array to $key
  }
  elsif($common{$key} == $mcc)
  {
    push(@most_common, $key);  # tack $key onto largest
  }

  if($common{$key} == 1)
  {
    $once{$key}=1;
  }
  elsif($once{$key})
  {
    delete $once{$key};
  }
  shift @nums; #slide down 1 digit
}

print "Most ($mcc): ", join(', ', @most_common), "\n";
print "Once: ", join(', ', (keys %once)), "\n";