File Coverage

blib/lib/Math/NumSeq/Kolakoski.pm

Criterion	Covered	Total	%
statement	36	56	64.2
branch	0	6	0.0
condition	0	3	0.0
subroutine	12	13	92.3
pod	2	2	100.0
total	50	80	62.5

# Copyright 2011, 2012, 2013, 2014 Kevin Ryde

# This file is part of Math-NumSeq.
#
# Math-NumSeq is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by the
# Free Software Foundation; either version 3, or (at your option) any later
# version.
#
# Math-NumSeq is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
# or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
# for more details.
#
# You should have received a copy of the GNU General Public License along
# with Math-NumSeq.  If not, see .

# http://dimacs.rutgers.edu/TechnicalReports/abstracts/1993/93-84.html


package Math::NumSeq::Kolakoski;
use 5.004;
use strict;

use vars '$VERSION', '@ISA';
$VERSION = 72;

use Math::NumSeq;
@ISA = ('Math::NumSeq');

# uncomment this to run the ### lines
#use Devel::Comments;

# use constant name => Math::NumSeq::__('Kolakoski Sequence');
use constant description => Math::NumSeq::__('Kolakoski sequence 1,2,2,1,1,2,1,etc its own run lengths.');
use constant characteristic_increasing => 0;
use constant characteristic_integer => 1;
use constant values_min => 1;
use constant values_max => 2;
use constant i_start => 1;

# cf A000002 - starting 1,2,2,1,1,
#    A006928 - starting 1,2,1,1,...
#    A064353 - 1,3 sequence
#    A054353 - partial sums
#    A078880 - starting from 2
#    A054353 - partial sums, step 1 or 2, is kol(n)!=kol(n+1) the 2 gaps ...
#    A074286 - partial sums minus n (variously repeating values)
#    A054349 - successive generations as big decimals
#    A042942 - something substitutional
#    A013949 substitute
#    A156077 digits ...
#    A078929 A(n+k) = A(n)
#    A081592 - runs of n many 1 or 2
#
#    A156253 kol supp
#    A064353 kol 1/3
#    A001083 A00002 lengths after iterating 1,2,3,5,7,10,15
#    A006928 lengths ...
#    A042942 1,2,1,1 lengths after iterating 1,2,4,6,9,14,22
#    A079729 1,2,3 starting 1,2,2
#    A079730 1,2,3,4 starting 1,2,2
#
#    A074290 - diff from n mod 2
#    A074291 - positions of n odd having 1 or n even having 2
#
#    A025142,A025143 - invert 1,2 so opposite run length
#
#    A171899 van eck transform of A000002
#
use constant oeis_anum => 'A000002';

sub rewind {
  my ($self) = @_;
  $self->{'i'} = $self->i_start;
  $self->{'digits'} = [1];
  $self->{'counts'} = [2];
}

sub next {
  my ($self) = @_;
  ### Kolakoski next(): "$self->{'i'}"

  my $counts = $self->{'counts'};
  my $digits = $self->{'digits'};
  my $pos = -1;
  my $digit;
  for (;;) {
    if (++$pos > $#$counts) {
      ### all zeros to pos: $pos
      if ($pos == 1 && $digits->[0] == 1) {
        ### special case i=2,i=3 digit 2 ...
        $counts->[0] = 2;
        return ($self->{'i'}++, ($digits->[0] = 2));
      }
      ### extend for get i=3 leave i=4 state ...
      push @$counts, 1;
      push @$digits, ($digit = 2);
      last;
    }
    if (--$counts->[$pos]) {
      ### non-zero count at: "pos=$pos digit=$digits->[$pos], remaining count=$counts->[$pos]"
      $digit = $digits->[$pos];
      last;
    }
  }

  while (--$pos >= 0) {
    $counts->[$pos] = $digit;
    $digit = ($digits->[$pos] ^= 3);
  }
  return ($self->{'i'}++, $digit);

}

1;
__END__