From: Victor Deryagin <vderyagin@...>
Date: 2011-12-17T21:28:21+09:00
Subject: Re: regexp detect repeating number

rubix Rubix <aggouni2002@yahoo.fr> writes:

> Thx,
> it works but I want to understand what does mean the two parts:
> (\d+?)and (?=\1)
> and what to add if I want to detect an exact time of repeating
> regards,

group (\d+?) 'reluctantly' (as opposed to 'greedy') matches some
sequence of digits.

(?=\1) performs look-ahead operation, which specifies, that to the right
of the first group should be it's copy.

To detect repetition count you can simply divide length of whole string
by length of repeating fragment.

This solution is simpler, a little more robust and refactored to
separate functions:

def repeated_digits(string)
  string[/^(\d+?)\1*$/, 1]
end

def repetition_count(string)
  string.length / repeated_digits(string).length
end

repeated_digits '252525252525'            # => "25"
repetition_count '252525252525'           # => 6

repeated_digits '123123123'               # => "123"
repetition_count '123123123'              # => 3

repeated_digits '1223122312231223'        # => "1223"
repetition_count '1223122312231223'       # => 4

# no repetition:
repeated_digits '123344453453454354'      # => "123344453453454354"
repetition_count '123344453453454354'     # => 1